B&Q have some for £79. We bought one from there this year for £99. Hubby decided we needed 950watts, 4 stroke. It works well, but it is very noisy to be honest.
Depends on what you want to run off it to how much it will cost, a 750W one ca be got for less than £100, the more power you need, the more it will cost
unless its a 5kw its not much good for anything bar an electric shaver ,few actually bare any relation to their stated output at least with 5kw you can run a micro and a kettle a the same time
thirsty beasts though even british gas doesent charge that much per therm (although they would if they thought they could get away with it )
Beware the cheap generators tend to leak and petrol does nasty things to plastic etc. This is my TV which was store near the genny after a recent trip. The blanket covering the TV to stop it getting scratched (lol) and the carpet have both melted. Don't think I will be using the TV again and the genny is staying in the workshop were it belongs.