I am sanguine over the suggestion that DIY "kitchen-sink developing" is 'cheaper' than commercial... these days, if ever, I think.
In years gone, it 'might' have been a bit cheaper, but by the 90's, the advent of the dry-to-dry 1hr mini-lab often meant it practically wasn't.
I have recently pulled my old dev tank out the cupboard to do a couple of rolls of B&W after my o/h & daughter had bee muttering they wanted to give it a go, and was pondering the matter of photographic economics of old! I was trying to remember how much it used to cost, and if my ailing memory serves, when I was a student in the early '90's, it typically cost about £10 a roll of 36, for a film + process & prints, if you went to Boots
B&W tended to be more expensive than high-street colour-print, and mail-order labs were often not a lot cheaper, but would give you bigger prints for your money, and/or a free-film of dubious quality! Slide film was cheaper, because it only needs developing, and I think that Jessops 'pre-paid' slide film, was about £7 a roll of 36; when shot you dropped it in the envelope that came in the box and they dev and sent back the mounted slides, you had paid for with the film. But then I recall ASDA doing a similar deal 'pre-paid' on colour-print film, for about the same price, at one time.
Cheapest way about it by far though was to buy 'bulk-length' film-stock and self-load it into re-usable canisters; I think that worked out about £1 a 36exp film, depending on what you bought; I tended to get 'cheap' slide film for colour and 'cheap' B&W; Colour-Print was a bit beyond the kitchen sink(after you had dev'd the negs)! But E6 chemistry for slides wasn't that cheap, and ISTR still worked out at around £3 a roll u-mounted, so it didn't save much very over 'cheap' high-street film and mail-order dev, really. B&W did though. But either way.. I don't think it 'saved' much money! I think like most, I probably spent MORE, simply because I 'felt I was saving money, and in consequence probably actually just shot more film! All good fun though.
In Y2K, I bought the dedicated film scanner I still use, as I had lost my dark-room, and looking at digital cameras of the era, they were expensive and / or no great shakes. On the economics I reckoned a film scanner, that delivered almost 10MPix resolution was still far better and cheaper than anything that took direct to digital pictures, and I could kitchen sink, cheap C41 colour-print film, as easily and more cheaply than C41 slide, and go neg-to-print digitally rather than in the dark-room... the wonderful leap to a pentium 2 computer with a 1.33Mhz processor and wopping 8Mb of RAM over my 'old' 90MHz Pentium 1 with its meagre 4Mb, trying to handle 10Mb fles from the scanner, however proved the futility of that plan! And its only in the last couple of years the computer's have caught up, and allowed me to exploit scanning software with the wonders of mult-pass scanning, ad 64bit colour depth! Great scans from an old machine! But I digress!
Economics of modern kitchen sink developing? I bought a set of IIlford B&W Chemistry in the summer, to teach my daughter film developing, I think for £25; 1/2 litre, at 1+9 concentration for 'quality' gives enough solution for about 15 films; at 1+14 for 'economy', offers enough soup for about 21 or 22 films, so costs about £2 a film. E6 slide chemistry, or C41 colour-print chemistry 'kits' are around the £40-£50 mark; solutions, if bottled and not cross-contaminated or anything can usually be used to do three developments, and f you are canny enough to batch up films to develop together like that, you might get 20-30 rolls from a kit, so again, about £2 a roll.. it's not a lot different to doing B&W....
And my local ASDA only charge £2 to do a straight dev-only on a roll of C41 colour-print film! (and an extra £1 to scan it for you)
So when you add maybe £10 to buy a developing tank, and anther £15 for a changing bag to load it, possibly more for measuring grads to mix your chemicals, possibly some concertina bottles to keep mixed chemicals in? There's little 'saving' to be found, even if you do enough films in your kitchen sink to defray the cost of the kit!
It IS fun, though! and as has been said, to soup a film, you really don't need much more clear space than to make a cup of coffee in the kitchen, and the 'stuff' you need packs away into a couple of shoe'boxes or a medium sized stak-a-box.
But you still want to make a 'display' picture from your negative or transparency. Colour printing has always alluded me; I do have a colour enlarger, but its a complicated process & I never had the patience or money to master it. B&W is a lot easier & simpler; but this does demand more hardware and more space; though under-stairs or 'cupboard' dark rooms used to be popular and didn't demand a spare room conversion; alternately, we used the bath-room; Piece of conti-board folded down on to the bath made a wet-bench for developing the prints, and there was usually enough room at the end for the enlarger on a upturned box.... curtain over the door and window to make it 'dark', and you changed the light-bulb to a safe light, often with an adaptor to power the enlarger-lamp, when you 'set-up'! But I have to confess, the 'faff' of trying to set up in the bath-room in a 'family' home, after kids had gone to bed, WAS main reason for buying that scanner 16 years ago!
Scanning to digital, does make t a lot more do-able; and cheaper Web-cam type film scanners are often under £30 or so, and while they tend not to offer the same level of detail you might get from a dedicated scanner that offers greater colour depth & such, for web-display and small-size printing, they are fine; cheap, pretty quick ad easy to use ad don't take up much space & personally I reckon I get better scans from mine than I do from ASDA.
If you WANT to DIY your own developing, then, as said, it is do-able; it doesn't take that much space or kit; but you do it because you want to DIY, not because it's going to be 'cheaper''; it probably wont be, and 'risk' you will wreck a film,from a loading error, mis-timing a soak, or cross-contaminating your chemicals, especially as you 'learn' the process, you are likely to waste a far bit to that 'learning' as well.
But, answering direct question; check out your local ASDA, other super-markets and high-street photo-shops & compare prices.
It's rather galling, now, to be being told that 'digital is so much cheaper than film'.... to think I can get a roll of Agfa from pound-land for a quid, and get it dev'd & scanned for another £3 at ASDA, to work out CHEAPER to process, now, than all the 'faff' of self-loading bulk film and kitchen-sink developing 'to save money' cost me quarter of a century ago! And get that with my old Olympus OM10 and a couple of good lenses, that all in might only be worth £40-50, or even my £5 XA2 compact, rather than the couple of grand of electric picture-making parafanalia sat in my camera bag!!?!?! Could have bought a LOT of film that could!!!