the 35mm f2 is something I've considered next to the 24mm 2.8 stm
I'm very happy with primes, my 50 1.8 stm lives on my camera, but I needed something wider
The EF-S 24mm STM is a super lens for it's size. I have had 2 as I passed my first one, as a loaner, to a family member.
I shifted to the EF 40mm f/2.8 pancake which I have had for a long while BUT very quickly found I missed the 24mm.
I bought another and with the £20 Canon cashback (ends on 31.8.16) it came in at £95. A bargain. Lightweight and fast (enough), it is in use daily. I have my full kit with me but I would say, most of my current shots are done with prime lenses. The exception is the 70-200L
So most used -
24mm/40m/60mm/100(macro) and 14mm (Samyang) on DSLR and 22mm on EOS M
Plus the Helios 55mm 44-M4.
I have the 50mm f/1.8 STM but it seems a littl too short some days and a little too long on other days.
Lately I have found/rediscovered a kind of 'retro' feel to how I want go shoot. The zooms are great but most of my current shoots are static and I have time and solitude to wait for the light and also use bracketing for 'safety'. If I was shooting moving objects that limit time to shoot, it would change the dynamics of my current photography. (As it did for a few hours las weekend).
At the end of the day it is about what you actually need and not desire.
All the lenses above were bought second hand except the 24mm and the 70-200). Originally the Primes were a bit of a throwback to my early 35mm film days when prime was what you started with. Now first choice.
Both the Sigma ART 20mm and 30mm lenses are glorious and I got the chance to try the 20mm for a couple of hours and the 30mm for a weekend. I liked them both and the 30mm is on my shopping list when/if I need i!
I have an old Sigma 20mm f/2 which I picked up in a s/h shop recently on my current trip in Ireland for €23. It is really for an EOS film camera (will not AF on DSLR) so I have 2 rolls of film sent off for processing from a day on myEOS 5 35mm.
I also have a Cosina 19-35mm EF mount which will AF on a DSLR.
The Helios 55mm 44-M4 is great fun for, usually, less than £30. The options are endless and are great for playing with light. I do cheat sometimes as I have a light meter but using your space tech DSLR with M42 lenses from a long time ago can be a real test for the photographer. I also still have my Pentax M kit from the 1980s. K Mount and as manual as M42 on a DSLR (and the EOS M. Some 28mm f/2.8 M lenses go for £25-40 on the bay in super condition. Worth a try, testing yourself with focal lengths you may find suit you while you save up £600 for a 20mm ART! That said a 35 year old s/h Pentax 20mm f/4 prime in good coddition will set you back £250-300, if you can find one. About the same for a 50mm f/1.2..... the very good 50mm f/1.4 between £75-120. Plus £5 for a K Mount adapter.
High end lenses were never cheap.
In summary, you don't have to bemoan and get frustratedat not having great quality glass now. Go retro while you save. Seek out the conversion factors for old glass so you can get the focal lengths comparable AND enjoy the challenge of learning with minimal 'on board' assistance.
I know a couple of pro photographers who use old glass, quirks and all.
Best wishes.
Steve