Biggest suggestion: When working on a tight budget, given to you by others, FIRST list out all prices! It really helps when budgeting. Also with only 500, I would try and find a cheaper electronics system. Also I would use some of your older parts, that are still in usable condition.
Suggestion: Come up with a plan that is very impressive, list all prices, and then show the sponsor and ask for more in order to produce a quality product.
Check your inventory for spare parts/electronics. If you have an extra control system (or don’t intend to keep your 2014 robot functional through the offseason), cannabalize that and use any spare equipment lying around. This allows you to use the $500 for adding cool functionality-- with $500 if you have an old chassis/control system/drive train you can use, you can easily do a t-shirt cannon, a boom-box robot with lots of lights, and have a bit for nice shielding.
If you can’t use any of your old components, then I apologize, but you’re out of my “FIRST zone” and into the hobbyist robotics zone, which I currently don’t have much advice for.
If you don’t have an old control system lying around (or just want something way simpler), 1540’s had a lot of success with the AndyMark Cheap ‘n’ Dirty controller. It’s a regular joystick controller that sends radio signals to a tiny box with 6 PWM outputs - plenty for our purposes, at least. It can be had for only $55 here.
You don’t need a driver station, laptop, or any software whatsoever to drive - just the remote, a few AA batteries, and the receiver.
One of our sponsors asked us to build them a robot for use at construction trade shows. It’s on a 2013 kitbot chassis with a control system that’s part FRC and part their products. It cost something like $1100 to build, not including their part of the control system.
It was a good off-season project and helped get the team up to speed for 2014.
I’m fairly certain that the VEX controller can be used to control motor controllers if you’re looking for something that can be programmed.
Mechanically some sort of arm is always useful and fairly easy to build. A t-shirt cannon is a favorite and the mechanism is really easy to build.
Careful with hobbyking. Shipping was ~6 weeks or something last time I ordered from them. Also, a lipo battery exploded and they said they only offer warranty for one month and did not refund or send a replacement. Yes, it says one month on the site, but it was a factory defect.
I also ordered a battery charger that was broken out of the box. Unless you really have to and can wait on shipping, then go with AM.