Heh, I've won that game a total of 6 times, first time being in October 2020. Don't know what to do with them, can't even find a selling price tag for it haha
There really isn't because only collector wants them, and I'm pretty sure that most of them who didn't have got one by now.
A site list it for 90$, some people on some sites are trying to sell it for 50$, other ones are trying to sell it for "offers". Nobody buys them.
Pretty sure that unless you search it very hard now it will be hard to get even 10$ out of it, 2 months ago you could easily sell it for 25/30$ tho, so if you really found 6 of them it was better to sell them as soon as you got them.
An item's worth comes from how much easy is to find it and from how many people want them, if nobody sells them the price may go up but if there's a big wave of keys (like from people who find them on the indiegala challenge) and everyone who wants them gets them, then well...
As I said before, never underestimate old removed games, search online if people are buying them or how much they're selling, even if they do seem bad. As long as it's a removed game, you can find a gem.