Honestly, just don't bid for 5* players at all. People bid themselves into crazy hemispheres all the time, up to the point where it's not worth it very quickly. Try to find some 4* or even 3* (if you got enough greens) fast trainers, which you can get for only 1 token most of the time. That way you can also buy 3-4 of the same position and see who trains the fastest without losing many tokens. There's nothing worse than bidding 30 tokens for a 99% player and notice that he's not training very fast or doing well in matches.