Looks like very few actually have come up for sale.
Note, on July 20th, the same laptop (albeit with a 512GB SSD) sold for $850
https://www.ebay.com/sch/i.html?_odkw=i7-6500U+GTX965M+alienware&LH_Complete=1&LH_Sold=1&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.XGTX965M+alienware.TRS0&_nkw=GTX965M+alienware&_sacat=0
The one that sold at ~$850 had a ~$150 SSD upgrade in it, so yours is not worth the same.
So $750 isn't an unreasonable asking price. I wouldn't pay it, but I'm sure there are a few people out there that would.
How have you tried to sell it? Locally is a limited market, whereas eBay (and similar) opens your market up to the world.
The problem there though is, with eBay, you pay a commission. Not 100% sure what it is on electronics, but for arguments sake, lets say it's 20%.
So, selling via eBay and getting your $750, then paying 20% commission nets you $600.
Remember, the one that sold on eBay on actually pocketed around $680.... so $600 seems pretty fair for yours.
So on that basis, you either need to sell it for $937.50 on eBay to net the same $750; A tough ask, I'm sure.
OR
You take your $750 you're likely to get on eBay and - 20% = $600, and try to sell it locally for $600 firm.
TL;DR $600 firm.