around 50 quid for the aerial), they said 100 or more just to get on my roof
Bearing in mind these are "Joe Public" prices, and an installer can undoubtedly find cheaper elsewhere; bog standard TV aerial about £11 or a really nice one able to pull in over quite long distances about £42. Very nice aerial cable, about 54p/m when bought on a reel.
Climbing on the roof is a dangerous task, particularly for older houses with steep roofs and maybe slates instead of concrete tiles, but unless there are real reasons to do so, it is often safer and easier to screw an aerial onto the wall of a house, rather than strapping it to a chimney. Wall bracket about £20 or a chimney mounting kit (you are not allowed to screw into a chimney), under £5 plus a mast of some description.
I've done a few DIY aerial installs in my time, but there are some roofs I will not climb on to - an aerial installer will have roof ladders; I don't. Our current house, with a low-pitch concrete-tiled roof is very easy and relatively safe :-)
And the point made earlier about monthly Sky or Virgin subscriptions is extremely relevant.