TUBoat

Hey,
I need some advice on what type of boat to buy. I am looking for a remote control boat that is between 2-3 feet. It needs to have a rudder. It also needs to be able to be modified easily, and by modified I mean I need to be able to take it apart and put equipment on the inside and then put it together again.
I am working on building an autonomous boat for one of my engineering courses. We are putting a micro controller and gps inside the boat. We also will be adding our own servos to control the rudder. We are trying to test a control system for an autonomous airplane that some other students are working on. The boat will be programmed to go to certain points in a lake following the gps system.
Any advice in a relatively inexpensive boat would be great. It does not have to be the latest or greatest boat. The most important thing about it is that we can modify it. We are more less just using it for testing.

Thanks!