NBA 2K19

at the moment there is only 1 Signature player avaliable - it's Kareem Abdul-Jabbar, who comes in 5 different editions (from 89 to 97 overall).
The cheapest one (89 Kareem overall) can be bought really cheap - for 5.000 MT points or even less, since the prices have dropped drastically.

For Numbered player (97 Kareem overall) you need to have 100.000+ MT points to win it by biding.

see the picture below:
https://twitter.com/NBA2K_MyTEAM/status/1060955231477891077

There are now multiple different signature players available on the market. If you search by signature series in the auction house, you should be able to find one for pretty cheap. I got a Dwyane Wade signature for 1500 and there were a few others at <3000. The achievement will pop after you add the card to your collection.