Good day mate,
Sounds like a second hand battery from battery world would work as long as it is deep cycle. As for a charger, you can buy a trickle charger for less than forty bucks. The question you have to ask yourself; "is this a sport that I can afford?" Another aspect is to improve your boat slowly and don't be in a hurry. This is one way to know if your really going to be going out on a regular basis, and not someone who dumps a bunch of money into a boat and then sells for a loss. Just my opinion.