go to your local bike shop and ask for advice, do not go to Halfords as they really only sell over-priced tat. Is your budget £200 each or total because if it's total you are not going to get a lot for your money.
I recently bought a bike for the first time since I was 14 and although I went to have a look in Halfords I soon walked out. My OH competes for our local bike shop so we went in there and I ended up spending £650 (double what I wanted to). Even my daughters bike cost £180 :-0. However with bikes you get what you pay for and the cheaper the bike the less likely it's going to last.
You also need to decide what kind of riding you will be doing, road, off-road, mixture of both as this will be a deciding factor on the type of bike you will need to buy.
HTH
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