Well, I can't really explain to you what the difference is since I personally have never owned a B3/T3. However, I do know that a few T3's still pop up from time to time at the track, and seem to run fairly well. But I have never seen a B3 in a race. If it has to come down to cash, then you either have to be patient, and wait for a good deal on a T4/B4(remember, I found my T4 on Ebay for $70, so they are out there for under $100) or go with the older T3/B3.
I would also suggest looking through the
for sale section of this forum. I took about ten minutes, and was able to find some pretty good deals on T4's, like this one...
http://www.rctech.net/forum/showthread.php?t=96339
Sure, it might be the RTR version, but in the short run, it would work fine, and would allow you to see if you really wanted to dive head first into off-road RC racing.
