At first i was gonna get the Cooler Master Hyper 212 EVO but its rpm is really low. What should i get for my Intel Core i5-4690K thats no higher than £25?
Depends on how hard you want to push it, but seen people getting 4.6GHz with very good temps with that CPU and frankly speaking, you will have a hard time going above 4.8GHz without a custom water cooling and to mention you probably can't stress that CPU that much.
Also don't forget that higher RPM in most cases doesn't mean better cooling, but higher noise level.