Robot Programming Kit (or something)?

Hello. I’m a high school Softmore. I recently joined First Robotics team 281 and am the programming sub-team. I already know a good bit about programming in general, but not so much about robot programming. Now that build season’s coming to a close I really want to start expanding my knowledge of programming robots so I won’t be as useless next year. Are there any good robot kits that one person can put together without too much trouble and then program (in C++ preferably) to do a variety of things. I’ve looked at Lego Mindstorms and similar products, but all of them either focus on the building part of robotics or use extremely simplified programming software with drag and drop code blocks. If there aren’t any good kits, are there any websites that teach you how to build and program a robot from scratch. I’m not looking for something that will take half a year to build, just a little something to work on over the summer. I know a lot of things like this are fairly expensive, but my family’s not too terribly tight on money and anything under $300 would be manageable. Thanks a whole lot!
Oh, by the way I only really care about the programming. If there’s a kit that comes with a pre-built robot that can be programmed, that would be perfect.

Here are a few options. The first three are Sumo bots and are a great way to go – get a couple and then modify their stock programming to include new strategies for manuvering each other out of the ring. Build a little ring out of plywood and have at it.

The last link is to a picture of my combat robot: Pneumo. (Pneumatic Sumo Robot – Modified Lynxmotion robot)