I understand what you are tr ying to do, but I don't know that you will save any money by hiring a driver .... you would have to pay him what he'd make as a taxi driver or car-for-hire in Athens, and for an 8-hour period that would be about €400, as far as I know ... and if you were going overnight, there would be that additional cost for a 24-hour hire, plus his meals and lodging. The CHAT tour is quite reasonable as those things go... check it out.
If you want detailed help on these forums, more information is needed. From your initial post, one gets the idea that you want to cover a lot of ground quickly. Now, it seems, you want to go slowly. Also, people inquiring about guided tours are usually not cost-parers, so it was hard to tell what you really wanted.
If you are considering D-I-Y, it certainly can be done, I've done it myself ... doing Delphi in an overnight trip, also going to Nafplio and visting nearby famous sites. You could do this on local busses, but you'd need to take one site per day, because bus schedules are not devised for tourist day-trips. And you can't get enough info on just a travel forum to DIY satisfactorily; you'd need to dig into guidebooks, find schedules for busses and ferries, study maps etc. I wish you good luck and happy planning!