[AlexMuir]

It depends on the level of comfort you want. If you're willing to shit in a bucket and shower once a fortnight then you can do it very cheaply and it'll be acceptable. Try that in a house and there will be concerns for your welfare. If you want a bathtub, on-demand central heating, a big fridge-freezer, bow thrusters, macerator toilets and a permanent mooring with mains electricity then you'll pay much more than you would for a house. Horses for courses. But doing things on boats is fun, and inventing solutions is great.

Edit: You wanted a figure - for the sort of boat you'll find on a canal in the UK. Bottom end: buy a small fibreglass boat for £5k, pay £1k a year for your licence (many at this end don't bother. Another £1k a year for maintenance and fuel )

Top end: Buy a big boat for £300k, £2k a year licence, £6k mooring, £1k insurance, £5-10k a year in maintenance.

Also factor in that boats mostly depreciate (though the last couple of years have been an exception). If you spend £100k on a boat today, you won't be able to sell it in 10 years get that £100k back. If you fail to keep on top of maintenance a boat will rapidly lose value.