I (we) started out with a 14ft Ouchita flat bottom boat with a 18hp Mercury. I was 14 and had money, but once we were done fixing/ tricking it out, the entry $ number doubled, and we got the motor for free!
I have a ZERO dollar (free) 1976 16ft Skeeter/70hp Merc in the backyard that runs and floats (or so I'm told), and I know once I get it wet, there will be a sucking sound coming from my pockets!
Start with a small boat to minimize damage. If you have never driven a boat, take an instruction class. Read up on maritime laws/rules, the coast guard and your state Parks and Wildlife should have all the reading material to get you going.
Be safe.