Well, you can check that out yourself on the website. First of all, you need to buy the game. Then you need to decide what kind of machine do you want to rent (1080p 60fps, 1080p 30fps, 720p 30fps) and how long you want to subscribe.
For e.g. the best machine you would pay for 1 week -> £17. For 180p 30fps would it be £9 and for the weakest machine £7. So in all, pretty expensive. There are similar services where you pay 10 EUR a month.