If you want a heart rate monitor with stop watch and GPS then nothing is that cheap, but hey that's an awful lot of technology on your wrist. I have the Garmin 410 which you can get from Amazon for about £150 and it's barely bigger than an ordinary watch. You can also use Garmin Connect to download all your run data to or even copy it Fetch Everyone. You can create complex sessions such as warm-up, intervals, warm down and it will set your heart rate requirement for each bit, you can download runs from other people and even pace yourself against a virtual runner. The 10 models (410, 610 etc) have much quicker to find GPS than the older 05 models (205 etc)
I used to use an ipod nano 6th gen. but even with all the calibration it's only so accurate as it depends on your stride length. I found that my 5k run was actually 4.85km, worse on hilly runs where stride is shorter. Bit of a shame as I realised I wasn't running as fast as I thought!
If you just want a HRM with stopwatch functions something like the Polar CX100 is about £50 on Amazon. For the best range of options go to heartratemonitor.co.uk