There are a lot of variables - car type, dates, status etc. I'd start with a general OTA like Expedia or Orbitz or maybe Autoslash and see what they show. Not every company has a one way fee every time. Then look at a roundtrip (depending on how long you will be gone). Airport parking would be high but a local hotel with a shuttle might be cheap and a roundtrip might be cheaper than two one ways.