The Cinque Terra Tour was 420 euros - there was only the two of us but it was a trip I wanted to do so I paid it and all private tours are in the 400-500+ range.
As they say, if you have more to share, the individual cost comes down - it went for about 9 hrs - no worries with making the ship 'back on board timeport departure - we had to be back by 5.30 and got back on board at 4.30.
I had no problems with making it back on time with any of our private excursions.
I do recommend Giovanni - brilliant guy.
We had a Merc car to ourselves but he also has a mini-van. The roads are not very wide in the Cinque Terra area.
Hope this helps