You owe it to yourself to just buy a 50mm 1.8. It's cheap, yes, and it feels cheap. It feels horribly cheap like some plastic toy that doesn't deserve to be on your camera. The manual focusing ring is horrible. The auto-focus motor is slow. You'll have instant buyers' remorse as soon as you feel its low build quality. BUT... that said, it produces some fantastic photos. I used mine reluctantly at first, but when I'd go back and edit a session, I'd find that 80% of the keepers were from that lens. It won me over in the best kind of way - with surprisingly beautiful images.
I was using mine on a video when it got hit and destroyed by a frisbee disc (those hard ones). It was sad, but it was $100. Life moves on. I used it for years before that, so my investment was a good one.
I have not owned or used the other 2 Canon 50mm lenses. I own the Zeiss 50mm 1.4 ZE, and I love it. I mainly use it for video though.
Here's an album I took years ago with my 50mm 1.8 right after I got it: http://www.daveheinzel.com/photos/?year=2007&gallery=81&pic=1386
Bottom line - buy the 50mm 1.8 and shoot with that for a long time before upgrading. Don't think of it as wasting $100 that you could have put towards a better lens. I never did.