general buying advice please

Hi,

I'm thinking of buying a new bike, and would like some general buying
advice. I currently have an ancient moutain bike with 21 gears - basic. My
riding is probably 50 miles a week at most, with a mixture of 50% off road
and 50% on road.

I've been looking at off roaders with suspension. I'm looking to spend a
minimum for something decent - maximum budget is probably £150ish.

OK, the assistant in Halfords (who was about 10) basically suggested all the
bikes with a big price tag. I accept that the really cheap ones are probably
best avoided, but would something around the £120 mark be suitable for the
miles/terrain I plan on doing?

Any advice appreciated - thanks,

David