The West Mersea Duck Punt is a brilliant and simple interpretation of a concept that goes back centuries and is highly relevant today. It's cheap, can be built in a couple of weekends and rows, paddles or sails brilliantly. Being light and efficiently driven means no need for an outboard. It's light enough to car-top and light enough to not need a launching trolley. Build one for under £100. Proper sails add a bit more.
Model radio-controlled yachts can be great fun and give you the opportunity to learn some sailing skills and techniques, and perhaps practice racing techniques and the rules, whilst not falling in, getting wet, or spending huge amounts of money.
You don't have to own a boat to sail. Why not sail with someone else who owns a boat.
There are some really very good low-cost dinghies out there.
If you don't mind some work, there are old and neglected boats out there which mostly just need some TLC. Though sometimes quite a lot of it.
There are small yachts and day-boats that cost only part of an arm and hardly any leg at all.
This site is mostly about sailing, but small rowing boats and canoes can give a great deal of pleasure and are also a great way to keep fit. Explore those little out-of-the-way creeks and streams. Get to the places the bigger boats can't.

Boats

A look at a selection of boats of different types.

I'm not yet sure how this will grow.