So you want a new Galaxy S5? Will new-ish be good enough? An eBay seller has a cache of open box devices on sale at a downright reasonable price of $429.99. This is an unlocked GSM handset, so you can use it on AT&T or T-Mobile in the US.
The model number is SM-G900A—so it's the AT&T version. Since it's unlocked, you should be able to get 3G (on 1900MHz) and 4G on T-Mobile, though. AT&T's version appears to have the necessary AWS bands. These devices come in their original packaging and include all the accessories. They're customer or carrier returns in like-new condition.
This deal includes free shipping in the US, or you can pay to have it shipped to a handful of other countries. There's no sales tax unless you're in New York. You get your choice of black, white, or gold.