Great idea and welcome to cycling for fun and fitness and, in your case, a very worthy cause.
Please don't buy a cheap bike. The chances are it will cost you in the long run, either because you don't use your bike because it wont run well, or because you'll be spending a fortune replacing and repairing cheap components.
This is an excellent article about BSO's (Bike Shaped Objects).
If you're going to be on tow paths and roads I would suggest a hybrid or even a city bike. You'll have a nice upright position which will be comfortable, and narrower tyres than on a mountain bike. That's important because while MTB's are softer to ride, so much of your energy is dissipated by the fat tyres and suspension that you end up much more tired than you will need to be. Riding on hard surfaces means you really don't need an MTB. You'll go faster on a hybrid and you'll probably enjoy the experience much more.
Go to a proper bike shop. They'll measure you properly, sell you a suitable bike that's properly set up and give you sensible advice. I think you need to think about paying at least £300 for a decent new bike that will give you many more years of enjoyment than something for half the price. At the end of the day, what's £150? A couple of days pay for most people. Cheap bikes are a false economy, really.
Good luck and enjoy it!
Please don't buy a cheap bike. The chances are it will cost you in the long run, either because you don't use your bike because it wont run well, or because you'll be spending a fortune replacing and repairing cheap components.
This is an excellent article about BSO's (Bike Shaped Objects).
If you're going to be on tow paths and roads I would suggest a hybrid or even a city bike. You'll have a nice upright position which will be comfortable, and narrower tyres than on a mountain bike. That's important because while MTB's are softer to ride, so much of your energy is dissipated by the fat tyres and suspension that you end up much more tired than you will need to be. Riding on hard surfaces means you really don't need an MTB. You'll go faster on a hybrid and you'll probably enjoy the experience much more.
Go to a proper bike shop. They'll measure you properly, sell you a suitable bike that's properly set up and give you sensible advice. I think you need to think about paying at least £300 for a decent new bike that will give you many more years of enjoyment than something for half the price. At the end of the day, what's £150? A couple of days pay for most people. Cheap bikes are a false economy, really.
Good luck and enjoy it!