two (well three actually) methods of working out how far you've gone - watches with GPS that rely on satellite signal to work out your location & route... Speed/Distance meters, which work out how far you've gone based on the movement of your feet, and lastly the good old 'measure it on a map' method - which is actually a LOT more accurate and easy to do than you'd imagine!
For GPS, I believe Decathalon do some cheaper alternatives, though I've no idea what their quality is like in terms of picking up a GPS signal... If you want good strong/realiable signal and don;t need a heart rate monitor, you'd not go wrong with a Garmin Forerunner 205. (not saying it's the only option, but one I know works well!)
For speed distance monitors, it's not something I've really looked into all that much - the best ones don't tend to be cheap, and as a result I'd rather buy a Garmin which can show me on a map where I've been. A cheaper option would be the Nike+ sport band which can connect to your computer and log all your details for you.
The last method is one I used for a long time when I started running, websites have evolved and the use of sites such as gmap-pedometer, and mapmyrun.com mean you can simply trace your route on teh screen and it'll give you a pretty accurate overall distance.
In terms of timing the run - I think any watch can do that for you, and it doesn;t sound like you need any of the 300000 lap memory functions, 32 alarms, 15 countdown timers etc... so just pick one that suits your budget and style
Hope that helps!
