Cardio over 100 is pretty rare. But you need to expend many green packs to get him at your level. 3 stars is a bit short. I have a very expensive 3 stars fast trainer and he can't keep up with the team. I'll finish his special ability and sell him.

There's a 3 star player in my market right now with a higher price tag than most 5 star players... lol. I'm tempted to buy him just to test his training speed.