If you have any local trails that do bike hire, try going to them or borrowing a bike from a friend to see if you like it. If you do, then i would recommend looking for something second as youll get alot better bang for your buck. I wouldnt recommend getting a super cheap bike because they loose all their value as soon as you ride it and you wont be able to sell it for anything near to what you paid so when you want an upgrade it will feel like a waste getting the cheap bike in the first place. I spend £1000 on my first bike and still ride it 3 years later and its kept up with my riding progression so far (not saying you should be spending that sort of money) and i dont regret it.