Go to Blue Nile and Old World Diamonds, and search for loose diamonds within the same range of specs as what’s listed on your appraisal. That will give you a ballpark of the current retail value, but that’s not the same as the resale value, which is the amount of money you can convince a buyer to fork over.
The caveat to all this is that without a GIA report, any ballpark figures on the retail value will only be as reliable as the appraiser, and you’re unlikely to find a buyer.
When I was consigning some things they would take about 30% of the valuation as the value. That's a rough guide. Given that yours is not certed it might be even less.