For Permit aircraft £20k will buy you a very good Jodel/Condor with a lot left over for contingencies. Or it will buy a half share in something modern, fast and economical, like a Europa. There doesn't seem to be much in between.
Direct cost of operating a Jodel/Condor is about £40/hour. With hangar and insurance you should be able to manage 50 hours a year comfortably within your budget of £5k, building up your reserves from the residue of your £20k for contingencies.
I can't comment on Europa operating costs except to say that the direct costs would be significantly lower based on fuel consumption.