Yeah I agree with the above post, if you get a fast training 18 year old 5* a few SP from 6* you can train him lots and use Green Boosters to make reach near 7* in one season, this way he'll stay a first team contender for five or six seasons.
Also for bidding bid at the last moment if nobody else is there. Never go beyond nock-out round 5 if you're on a 35T budget. If other people are bidding check their stats, see if they have lots of scouts and cash, they could be a T buyer. Always bid for 5* after Lv 3 because the 3* and 4* will appear as 5* for lower players and you will get in to bidding wars for bad players, in the earlier lvs get some old 5* and one or two 18 yo players and save your T for lv3