Geico supposedly pays "Actual Cash Value" in the event of a total loss - i.e. the fair market value of property; which is essentially replacement cost less depreciation less your deductible.

Don't know what 'database' they use to determine 'actual cash value' for your area but they should be able to back it up. Get some listings for comparable models in your area - the difference betweeen the two should not be huge.

Always argue with the insurer. I've been down this road before and the final offer was very different than the first lowball.

Good luck