I was also going to suggest freecycle.
You could always convert a bird cage, so worth keeping your options open
Have you any car boot sales still going on around you, normally hardstanding ones carry on a little longer into the year than the ones on fields
Have a look through freeads, preloved, adtrader, gumtree, clickpets etc
Have you tapped "cage derbyshire" into your google search engine.
Can't think of anything else right now.