I havent checked since the panic buying started but eBay has several vendors selling complete Gen 3 Glock 17 slides for under $250.oo. NOT Glock factory uppers though. I think Rock Island. They look nice with lightening cuts!
If you want a pretty solid slide for a decent price look at the brownells glock slide. I’ve had two now and I have nothing but good things to say about it. You can get it with front serrations, top window, rmr cut and it’s like $190 for the slide. I can meet up with you and show you my g17 slide that I have on a polymer 80 build. 1000% worth the money.