There's no denying it, even cheap guided tours are going to cost more than independent trips. Some guided tours can be very expensive, so be sure to compare prices. I've also done private tours and they're absolutely amazing. It's also much more expensive, of course.
The two reasons why I probably won't book a group tour again are the people and the tour guide. However, with that said, I really enjoyed our tours (on separate trips) of ancient Rome with Through Eternity and Angel Tours. I think that as the applications get better and better, they will help the tourism industry and it is advisable to take a look at them. You can get all kinds of maps, bus schedules and restaurant guides for a fraction of the cost of tourist books.