They said it. It's about your personal value for money -but spend as much as you can afford.
Everyone has different values. For example..... we were just in Rome and took a day trip to Pompeii. We've always been DIY/explorer types, but mooted for once just joining a tour and not having to worry any more about it -something which would generally have been out of our budget on most other trips. But as we looked into it, you only got 2 hours on site, "bathroom breaks" turned out to be commercial opportunities for vendors in bed with the tour company, more time was spent on the bus than anywhere else..... So we forked out big bucks to take the bullet train by ourselves and got 7 hours in the ruins, no sidetracks we didn't want, 1h 10 minutes each way @ 299kph.
We didn't spend an awful lot less than we would've on a day coach trip. But we were not disappointed.
Figure out how much you can afford to spend then see what you can get for it. Then compare those options.
Get some guide books from the library, see what they recommend vis-à-vis tours worth taking, sights not to miss... then see what packages you can find that include those things, contemplate how easy/much fun or not it would be to do it by yourself and that should give you a better idea of where your values lie/what is the type of experience worth paying for and what you could honestly miss and not lose sleep over. then see what really fits the bill and the budget.