An 07 Z with that kind of mileage could easily go for about $45k depending on the options it came with. With that being said, I wouldnt buy any Z before 2008. They upgraded from the T-56 to the TR6060 tranny that year along with some interior items as well. Also, there was a lifter issue with the 07's, it was a very very very very small amount of LS7's with this problem, but still, you should be aware of it if your looking for an 07 Z. If you have the money to spend, your better off getting an 08 for what you would spend on your buddies 07. If you have a little more, get an 09, they upgraded the oil capacity to 10.5 qts, same as the ZR1.
Personally, I wouldn't get a Z before 2010 since they swapped a few drivetrain items for those in the ZR1 that year. But again, that depends on the budget. Hope this helps.