The 5700 and 5700 XT won't be coming out for another week, so you would need to wait at least that long for those cards. And since there are currently no reviews available for them yet, it's not possible to say with any degree of accuracy how well they will perform relative to the other options. And rumors are that the RTX "Super" cards will be announced in a couple days, even if they probably won't be coming out for some weeks. That might potentially affect pricing of existing cards though.
I'm not sure that I would go for a used 1080 Ti, since it will likely not be covered by warranty, which could make it a bit of a gamble considering the cost of those cards. It would probably be the best performer for the money in most existing games, but if raytraced lighting effects take off, it will likely fall behind the 2070 with those enabled.