I would say if you're not in the position to try and make a competitive one, go for something that you can have a bit of fun with. I would suggest something like that chassis you have with exposed wheels at the ends, have a big ground clearance so you can almost drive up and over other robots, it won't get stuck on walls etc, as soon as it's flipped you can drive away, and it would be a lot of fun. My new one was built for our smaller shows and designed to be as simple as possible, but its design makes it great fun to drive even though it will probably never win a fight.