If you are just riding for fun and exercise or to get somewhere and not racing, shaving split seconds off your times or worried about keeping up with the latest and greatest, the easiest and cheapest thing to do is probably to switch to friction with any long cage derailleur and then you can you pretty much use anything you want with anything there is. Really, you just need to match the chain to the cassette and everything else should work just fine. It is so liberating!