Assuming it is just the Deck and the case, with no extra accessories or upgrades. $280 would be the absolute max. It also better be nice and clean with no blemishes for that price, and the battery would have to be with 2% of 100% life. I know the refurbs are $280, but that also isn’t after tax and there’s a small gamble of getting that is defective once you receive it. At least with a person selling it, you can test all the inputs and check temps in a game pretty easily.

https://www.reddit.com/r/SteamDeck/s/9eKfcysRaA price guide

$150