The tiers of player cards you need are:
- Pink Diamond
- Galaxy Opal
If you think "there's no way I can get this..." now is the time to do it. My strategy was to sell all my cards to get MT points (except one in each category). This includes coaches, shoes, badges and everything else (except Contract cards...see below). I sold most of the cards red or lower at the default price but if you want to maximize profit, start an auction for each one.
Then keep three cards you want to play with. If you are starting from scratch, my strategy was to use a two-way point guard, a three and D player, and a post player. If you start with nothing, an example team would be a Ruby PG, Ruby Klay Thompson, and Gortat or Anthony Davis or Boogie Cousins. Whatever players you choose, all players should have at least gold Defensive stopper, Gold shooting badges (except maybe the big), Gold Dimer Badge (including the big). For non post players, I looked for at least 90 in speed, open threes and lateral quickness. For my one big guy, I used Diamond Anthony Davis for a long time before I got Chamberlain, although I use the post consistently, Someone like Kevin Durant may work better for a team that relies on threes.
My final team (all purchased for under 35,000) were PD Wilt Chamberlain, PD Gary Payton, and then either Diamond Kobe Bryant (HOF Defensive Stopper), Diamond Dell Curry (fairly fast and great at threes), or Diamond Andre Iguodala (good at defense, shooting and dunking). Then you just play Triple Threat against the computer to slowly grind VC. You get 300-400 MT per game, but other than playing the Auction Game (buy low sell high), you are guaranteed to increase your MT.
In the end, I bought a Galaxy Opal player (I can't remember who...I sold him immediately after the achievement popped), for about 120,000MT. As time goes on, the price of Galaxy cards will undoubtably drop too. Good luck!