If you don't need lots of boot space you could look at a Citroen C1 - £40 per year road tax, 50+ MPG, lowest insurance group, and you'd get a brand new one with a 3-year warrantee for your trade in and about £5500 or so.
It could be that there's moisture in the cooker control unit, always a possibility if it's near boiling pans - I'd check that first if the trip still operates with the CCU off