Insure the ring/stone ASAP. Usually you can get a rider onto an existing homeowners or renter's insurance policy. Your jeweler should provide an appraisal which will value the ring for insurance purposes.
Was well worth it when our ring was damaged accidentally. Saved a couple thousand dollars in replacement costs.
My other advice was that you can usually negotiate a discount if you're willing to pay cash. Again, this was NYC, but I think it'd apply everywhere.