Based on the internet prices in Pricescope database 0.77-E-VVS1 AGS0 (with AGS report) can cost from $5250 to $5750.

If the stone has AGS0 proportions but other than AGS grading report, it can cost about 10% less.

If you aren't buying over the Internet, the price can be 10-30% higher. That might be reasonable if you are getting good additional service.

We can tell you more if you'd give us more details on the stone: Grading report, Crown and Pavilion, etc.