How to find free or affordable rehearsal space
Look around you next time you are passing through your local city, town or village. Make a note of every bar, pub, cafe and restaurant that you come across. You might not necessarily consider these places as ideal "rehearsal studios" but they may have available spaces and a willingness to lend it to a deserving group of artists such as yourselves.
Remember - these companies are set to benefit from this arrangement too as it is fantastic for their PR to be seen to be working with and supporting local, independent artists and community groups. They are also set to gain profit through the increased footfall as long as you and your colleagues buy a coffee or a pint or a bagel or something.
You might have more success with independent businesses (who aren't bound by the same corporate rules that the big chains are) but big players such as Wetherspoons might also be worth a shot. Try offering free music, poetry or scratch nights in exchange for free rehearsal space at their venue. You could also mention from the beginning that you would be interested in holding monthly socials for friends, family and followers of your company.
Libraries often have meeting and conference rooms available. If you can prove that your project is involving or benefitting members of the local community and that you are working on a tight budget then they are unlikely to refuse! I happen to know that Newcastle City Library are very accommodating.
From personal experience, the key to winning yourself some free rehearsal space is charm. Be charming, be confident and be polite. Set up meetings with managers. Speak over the phone or in person rather than e-mails which are easy to ignore or delete. Make your project sound as big and important as it really is!