Forerunner 110 - just over £100, or go 2nd hand. Some use their smartphone but I've no experience of that.
Other option, just get a normal stopwatch - we all used to use them perfectly well before GPS!
You can team that up with websites such as mapmyrun, or fetcheveryone, and get a pretty accurate measurement of your course either before or after you run. If you regularly run the same rout, you won't have to plot them out so often. The only downside is that you don't get "on the fly" pace feedback, but I just used to have a watch which recorded multiple laps, and just had set points on each course where I pressed lap, and so knew whether I was on pace or not.