Gpu help and depreciation

[Raging-Storm]

I am looking to buy the 1080 ti straight from evga for 710$.    If new cards are announced next month how much value does that make me lose on the card. I see these selling used on ebay for 650 to 600.    They are usually 800$ new just on sale for the 19th aniversary sale.  I have no problem paying retail for a 1080 ti if it just released but conaidering its almost 2 years old i want to look at deprecation as id like an 1180 ti. Problem is my card died and im using an ancient  560ti ?.  How much did 980 ti sell for the day 1080 ti released.   This will be my first higher end 8 srries plus gpu purchase. I usually bought 6 series cards