It is possible to get an ISP to host your site for less than £100 per year, usually with unlimited number of e-mail addresses and mail forwarding but the rate is actually depending upon how much your site is accessed by visitors so if you had several thousand visitors a day, the price would be higher than that.

If you are running a site with a database connection and/or e-commerce capability the cost is a lot larger and would be from around £100 per month and upwards.

A crude rule of thumb for the maintenance cost of a site, i.e. keeping it up to date and giving it a "face lift" every now and again is to assume the yearly cost to be half of the initial design cost.