Built outta spare parts and a foam kickboard.
Me and my dad run these little quick $60 race boats we found on Amazon. Problem is, the run time is only about 15 minutes. And the low voltage warning gives you about 4 seconds of warning before shutting down.
I've gotten good at timing it with 15% of battery left. But I also don't like jumping in a pond if I screw up!
Edit: for thoes asking this is the boat I specifically ordered, but just searching for rc boats on Amazon there are a large variety of these in the 60-80 dollar range. They're mindblowingly good for the price too. 540 motor and lipo powered. And can recover from capsizing!
EDIT2: I took her out on the maiden voyage yesterday evening to see how it does. I was a little too worried about maintaining correct balance, it floated pretty well, but when you went quicker than a crawl, it starts to dive and wash the deck out. I'll be moving the battery behind the motor, and adding some of the scrap foam pieces to under the front forks to keep the front end out of the water more. That should allow it to move at speed but still easily catch and push boats to shore! I'll share some pictures when I get another good weather day to drive it!
But there are tons of other styles in the 60-80 dollar range just by searching for RC boats.
here's the one I bought myself
Here is the slightly smaller one my son owns
and the one my father purchased
The rc racing boats me and my father have are both "flipped" something or another brand. It's from China and there are a ton of resellers on Amazon when you look up rc racing boat in the $50-80 dollar range.
But there are tons of other styles in the 60-80 dollar range just by searching for RC boats.