There isn't a good price on 1080Ti but the best price recently is that Gigabyte Aorus GTX 1080Ti @$659 on massdrop:
Aorus GeForce® GTX 1080 TI 11G
Not sure if it's still alive, however.
If you need to drive 4k then yeah..that would be the deal. If 1440p and some 4k, the best bang/buck card right now is the 1080 and I saw one today on Slickdeals for $478...also dont' know if that's still alive..you'll have to check.
GPU's are still way overpriced right now. I just built an X370/Ryzen 1600 rig with a GTX1060 and it costs around $1100, that same PC cost $1000 w/1070 a few months ago, granted it's not all the GPU it's a combination of memory, SSD and GPU pricing.
Having said all that, i'm seeing 3rd party regularly go for $700+ on the forums, Hardforum, ebay..etc.