Regardless which brand/style/length you opt for, a $15,000 boat can turn into a $30,000 boat in less than a months time. And after all of that money is spent, you’re still left with a $15,000 boat. I’ve done it, as have a million other boat owners.
First, make sure the boat is structurally sound. Replacing a rotting deck is not cheap!
Second, investigate the condition of the fuel tank. Most boats don’t have access lids on the tank, so you’ll have to rip out the deck if the tank turns out to be bad (which takes you back to my first point).
Third, pay close attention to the drive train. Inboard/outboards are cheaper to replace than outboards, but you’ll still be out at least $6,000 if you have to replace a motor, and even more if you have to replace an outdrive.
Honestly, that’s the most important stuff to worry about. Buy a boat that is structurally sound, with a good fuel tank and power, and you’ll be spending quality time on the water right out of the gate. Too many people are worried about electronics when buying used boats. They’ll skip on great boats just because the electronics are dated, and instead buy boats that require repairs that will cost 3X as much as new electronics, simply because the fish finder is new. A quick search in the classified section will produce entire used electronic packages at really cheap prices.