Youth Players: Should be free. The players that come through the youth system aren't good enough for most teams and are usually sold on the transfer market straight away, whos going to pay around 20 tokens for a 3*/4* youth player? Cheaper and better players on the market. Arsenal didn't have to pay anything to get Jack Wilshere, they just offered him a contract when he came through the youth.
Personal Trainer: Yes this is expensive but like you mentioned you don't need to use it on your lower ranked players, this is best used on high-end 5* 18-19 year olds OR high-end 6* scouts 22-24 year olds, meaning your making your current best players even better. It is better to invest your tokens on green packs instead of personal trainer and just power train your players, you would get more skill points that way for your tokens but you will get some injuries in the process.