Assuming you want to eventually become Tamiya compatible, you can't go wrong with the Imex Model Company in Florida. Taigen and Torro tanks in IR that you can use with the stock system to start and then later get into new boards and Tamiya compatibility.

Another way to go may be this ... since there are several of you, get the lowest price all plastic Taigen or torro tanks you can right now and have fun playing around with the stock system. Just go straight out of the box and get to blazin' at one another. Then you each get the heavier, more expensive tanks and concentrate on making those Tamiya compatible. That way you all get to play right away and you can take your time making the switch to more sophisticated stuff.

And if you guys get together and order several tanks at once you'll be surprised how well Imex will be able to do for you.