for American prototypes, there are NJDOT Arrow Is ( discontinued), SEPTA Silverliner IIIs, (IHP) and Metroliners (Bachmann) available, as far as EMUs go. they are all still pretty expensive,and the first 2 need to be assembled, and some i don't think come with pantographs.
The metroliner dummies are cheap, but powered cars are next to impossible to find, that is, unless you want to build alot of money one ebay for one. in the end you would get the power car for cheaper than the other EMUs, but you already probably paid more than it the powered metroliner costs.
I know IHP makes the NJT hudson bergen light rail vehicle.
IHP's site is here:
http://ihphobby.tripod.com
IHC (yes, the companies get confuseing) makes a san francisco municipal railway light rail vehicle.
i thought i saw a DMU that was going to be made, but i can't remember where.