If you want a cheap option just for reviewing a run up a hill climb or sprint then I can recommend a £50 option from amazon that I used last season. Comes with mounts, spare batteries etc all in for the price. Obviously nowhere as good as a go pro, but if, like in my case, you're watching it back on the screen straight after a run to work out why the time is so much slower than everyone else, its a good bit of kit for the money! Alan B uses an old iPhone for the same reason which also works well, and with much less faffing than other options.