Even stretching to £25,000 will only get you a very low end steel narrowboat which would need work, so I'd definitely suggest you need to secure finance for a decent boat. £35,000 - £40,000 gets you a perfectly good albeit old boat. If you want anything built in the last 20 years that is suitable to live on, you're going to have to spend north of £50,000. Of course financing this sort of sum in addition to mooring fees/licence/boat maintenance/boat deprecation, will probably be close to what your current rent is.
The sensible advice would be to use your cash deposit to buy a flat/house.....long term it's by far the better proposition then buy a boat as a hobby later...........But you only live once.