How much should you spend?
The answer to this question depends entirely on your budget.
If you are looking for a high quality watch then you'll have to be prepared to spend a little more money. Remember though that high end watches can cost thousands of pounds, but if you get it right they can be a good investment.
If you intend on spending less money then don't expect to get a high end watch and it won't last long. But if you want to get a good quality item at a reasonable price, consider purchasing a middle-of-the-range watch.
You can purchase watches online as well as from specialist watch (and jewellery) stores in the high street. Have you considered buying a watch from a friend or family member?