Some advice I got a while ago that helped me was to save actual contracts for my top tier players.
- Save your best players for online challenges and the high difficulty offline challenges. Use your contract cards on them only. Preferably amethyst tier and higher.
- Make a separate squad for easy offline challenges full of bronze, silver, and golds that you can win with and refill their contracts with the mt you get from those challenges. They are cheaper.
- Switch out bronze and silver role players when their contracts run out to save even more mt. Reward cards acquired with tokens can also be swapped regularly.
Once you get the formula down you build up mt and contracts in no time.