That's what I do and the prints cost 10p. One of things that niggles me is that they got the info for nothing in the first place. So be prepared for long pockets, alternatively long hours.Edited to add:
Some libraries allow free access online to Ancestry 'Library version', which is limited and sometimes slow but you might be able to get the set of records you need for nothing.
It's also worth knowing that there is now access to the 1939 register which was used to award rations to civpop and it bypasses the restrictions for the 1921 census. Long long trail assisted me in finding a marriage I never knew had happened and subsequent offspring. I also got copies of original documents about deaths by bombings that the council were responsible for there and Voters roles and Gazetteers. These allowed me to track movements. The only thing that stumps me is finding out if some one served without any other details.
Last suggestion, plan. Don't make search criteria to wide concentrate on one person. You'll be allowed 1 hour on some library computers so list what you want to check