Help finding a cheap kindle fire hd keyboard?

I'm looking for a cheap keyboard preferably in a case for my Kindle Fire HD 7" (sorry not sure what generation it is but it's at least a year old). I've found loads of cheap cases on Amazon around £6-10 delivered which would be ideal but it seems as though none of them are compatible with kindle as they don't support OTG technology, so frustrating! Has anyone got a keyboard that works for their kindle fire they could recommend?