For that price range there is a lot of junk out there that if something does happen you might as well toss it in the trash. For $150.00 though you're not going to get blazing speeds but in the 15-20 MPH range. AquaCraft and ProBoat both have some in that range and you can get parts for them.
Don't let kids underestimate you as they catch on quickly. My son was racing RC trucks at 6 and getting trophies against adults. I let him race a nitro outboard tunnel at 12 and he got a 3rd place finish in his 1st race. You can limit the speed though if you feel he needs to go slower.
No reverse in a fast boat.
Wash it down well after running in saltwater. Shoot WD-40 or something similar on all metal parts.