I find this is enough for e-mail but is too slow for web browsing unless you turn off the images. On the Orange ED50 tariff you get 50 minutes of off peak calls per day included in the line rental. Go to the Drifters website and fill in the form. They'll post you a brochure. Drifters is a well established federation of the smaller boat-hire companies one of which is my cousin Susan's firm Shire Cruisers at Sowerby Bridge in Yorkshire.
Prices vary a lot.
A new narrowboat built to your own chosen layout might cost 50,000 Pounds. As the boat ages its value falls and there are good second hand boats available for 20,000 to 30,000 Pounds. Narrowboat prices seem to decay with a half-life of roughly 10 years. If you buy a car there is a registration document. If you buy a house there are the title deeds.