A full set of inks for my A3 Epson is £80-90 and of course there's paper to buy too. I think I worked out some time ago that an average A4 print costs about £1 but I've probably under estimated it, probably by quite a bit.
Home printing isn't cheap and you can probably get your prints done online cheaper but there are non cost advantages to home printing which IMHO include being in control of quality (I've only ever paid for one picture to be printed and it was a total waste of money) and being able to produce the prints as and when you want them. You'll have to make your own mind up if home printing is financially sensible or not and if you're willing to pay more to be in control.
One thing I'd think about doing is going for the two printer solution and getting a document printer (laser?) and a cheapo photo printer, the £50 and under variety sort they sell in supermarkets (Canon, HP, Epson etc.) If you're going to be printing to a maximum of A4. My sister has a cheap supermarket bought one and the image quality is IMO good, I don't know how it'd stack up against my printer as I've never printed my shots on her printer or her shots on mine but the shots she takes (with a compact camera or smartphone) and prints certainly look more than just good enough.
I think I'd prefer a cheap home printer to ordering online simply because you can then print as and when you want and have the results as fast as you can process and print them.