Nope. You must consider raises.
After 35 weeks, my trainer will cost approximately $31,000 weekly. I generally consider selling at closer to $40K weekly. Then the calculation is simple: Because trainers' salaries increase by a set percentage, the higher the trainer's salary, the more rapid the increase. Thus, my trainer at $16K will always cost a minimum of $34K per week less than a guy who makes $50K weekly. In other words, even if the difference in the up-front price is $500K, the $50K trainer costs you that much in weekly salary after just 15 weeks. Meanwhile, I can keep my trainer for 45 weeks and he still won't cost me $40K per week.
So it's far more cost-efficient to buy a cheap trainer for more money and just hold on to them forever. That also avoids any uncertainties in the auction process, and best of all, doesn't carve out as much money from your weekly revenue, allowing you to support more talent. It's true that you have to occasionally set aside money for a new trainer, but it's not all that burdensome to come up with $500K.