You're not really going to get a decent "cheap" monitor. Around £150 is what you should expect to pay regardless.
The first thing I would do would be to look at the back of your PC and see which connections are on there. If it definitely doesn't have DP I would be both surprised and a little disappointed.
The first thing I would do would be to look at the back of your PC and see which connections are on there. If it definitely doesn't have DP I would be both surprised and a little disappointed.