garge or unit

I'm near Plymouth in Devon, so probably prices here are similar to Somerset. In the city you are looking at about £80 per month rent for a single garage in a block, generally without electric/water. You may be able to find them a bit cheaper in the small towns although they are not easy to come by. For example, I currently know of only two private garages advertisd to rent in Plymouth, for a city of 250,000 people. If you want to find a garage in a town/village, you will probably need to put up flyers etc.

I rent a small industrial unit from the council for my business. It has vehicle access and space for about 4 cars comfortable/8 cars if you don't need to get in to them and can stack them nose-to-tail-to-wall. It's the typical size small unit that is available round here, and they come out at about £500-600 per month, excluding VAT, rates, bills etc. So they are usually outside the realms of a hobbyist, and the council usually won't rent to individuals. Other landlords are sometimes less fussy though. I do occasionally see small units come up on farms or small industrial complexes in villages etc that have been built on former farm land. These are usually quite a bit cheaper but you should still probably budget £500/month after all bills.