When the dolly 'rolled off the track,' did you make sure the track was straight? Usually when that happens, it means the track itself isn't straight, though it is also possible that it was due to your DIY abilities
When I was at film school, we had Wally Dolly and Digi Dolly dollies. The tracks for which aren't really great, especially where the joins are. The benefit of PVC pipe is you can get the length you need without having to join track on a low budget. Expensive track (I'm talking thousands per foot) joins together beautifully, but one foot of that sort of track is way out of your budget range.
I might look into something like this (or machining something similar):
http://wallydolly.com/store#!/Wally-Dolly-T-Section-Only/p/10027269/category=2334126
And using PVC pipe as a track. If you
needed a platform you could slap one on top.
Also keep in mind that the quality of movement is only as good as the person pushing the dolly. The better (more expensive) the dolly is, the easier it is to get nice movements. The dollies I generally use have the camera attach to the dolly itself, and you ride on it and can operate the camera whilst the dolly grip pushes the dolly and operates the boom.
With a cheap dolly, it's often very difficult to ride on, and especially very difficult to operate whilst moving. If you're the only one there, you'll need to push the dolly. If you have someone else to do it for you, you can attempt to operate. It takes
a lot of practice to get smooth and consistent speeds. That's why dolly grips exist and get paid what they do.
That's not to say you can't get usable/acceptable shots out of cheaper systems, just that I wouldn't expect high quality dollying out of a $600 dolly system, DIY or otherwise. Used Panther dolly kits, for example, can go for $50,000, and that's without any track!