If the budget is only 5 bucks then you maybe in trouble as i'm sure your going to have to try a few diffrent ones before you find whatever suits your need the best. I do recall reading in the Mini Rio thread about some guy named John thatssome kind of an engineer and he supposedly can steer you in the right direction when it comes to prop set up. Im newish here (to boats as well) so hope my info is good for your project.

Rock On!!!
JRockZ