Hi,
I'll give my opinion to your issue!
Salary of my courent trainer is 42 k he is lvl 5 trainer.
It all comes down to mathematics. If I remember corretly, the lvl 5 trainers' salary increases by 2% regardless of the old salary. But you need to consider how much you're spending on your new trainer and the old one, the sum total. I recommened using buzzer-manager.com as it has a good staff management function that can help you, this example is from there!
IF you change your trainer from your 42k lvl5 to 25k lvl5 trainer for 500k investment, then after 20 weeks the situation will be:
Total price of new lvl5 trainer: $ 1097971
His salary after 20 weeks: $ 30504
Total price of old lvl5 trainer: $ 934035
His salary after 20 weeks: $ 51247
Difference IN FAVOR FOR the old trainer is: $ 163936
So, even after 20 weeks (that's almost 1½ seasons!), the older trainer will be cheaper on the total costs. I personally get myself a trainer that doesn't have a high bid on him (1k-50k) and then change him away to a similar kind about 1-2 times per season.
So I would recommend you to check out the TOTAL costs for changing trainers in a course of a season or so. The cheaper total costs, the better option, in my mind! (y)
Hope this helped on your decision-making!