Hi! Since you'd be in Vegas for only a week, I wouldn't advise you to go look for consignment stores. Most tourists just hang out on the Strip and rarely gets to see any part of the city where the locals actually live.
And while it's ture you can score something nice from consignment shops, they would be full with things you wouldn't like most of the time. You mentioned the lower price points, and that part isn't so true. I've seen lots of places asking for much higher prices than eBay. So to go out of your way and find nothing you want to buy would be such a waste of time taken away from your vacation. I'd rather just check out the malls and shops in the Strip.
Lastly, I've been to several consignment shops in London and even bought a Chanel bag from one of them! You should search if there are some around your neighborhood.