The check engine came on in my 2000 corvette and the diagnosis was a evaporative

Yes, for the most part, the evaporative emissions system will not affect vehicle running condition, but does affect the vehicle's ability to reduce fuel vapor emissions. How much it will cost - depends on what is found to be failing, which requires testing the you'll likely have to pay for as well. Check with some shops near you to get an expectation set on what will happen and how much it will cost. www.repairpal.com/repair-shops