Any cheap, basic swimming pools in Budapest?

Hi,

I will be here studying for the next Protected content and want/need to do some exercise while here to counter the effects of the food and cheap beer that I also want to enjoy.

Aside from the spas with their pools, which are not cheap and not really for swimming as proper exercise, are there any ordinary public swimming pools (like council-type facilities in the UK) that I could use while here, either by joining or on a pay-per-visit basis?

It's not the sort of thing that's easy to research / find, so any advice would be appreciated. Cheers!