In that condition not a lot. However, cleaned up, lubed, new brake blocks, new brake and gear cables and a good spray of detailer it's not a bad bike. Done up I'd say maybe £75 - £100 tops. It's very dated by today's standards, that's the trouble. You might have trouble finding a buyer. In it's current condition maybe £30 - £40. That chain would put most buyers off but scrubbed up and lubed it might look ok and even work.