thanks for the input..
Yes, I did consider putting growth rates and other things into this...but it would start to get complicated for a "basic" method. This basic method is the "jumping off" point for anyone to use and modify for their own uses.
For example, growth rates....these engineers repair stat growth rates in this example vary from 3 to 6 points per lvl. You are correct that one with a high growth rate would be more valuable in the long run. One could project the True Ability out 10 or more levels. Further, one could consider adding more experts or vets into this projection and then determining a value based in what one believes the engineer will be. This is known as predicting future value.
One could "weight" the factors that are felt most important. Is growth rate more important then ability or at least it should be considered? If the user thinks so, then the cost per point could be modified by a factor that the user feels is correct. A + 10 growth rate might reduce the cost/point by 10 % while a +5 growth rate reduces cost/point by 5%. A user is free to use what ever number he desires.
In the example given, the lvl 81 engineer has a per lvl repair growth rate of +3 while the lvl 80 eng has a +5 repair growth rate. If you feel that the almost twice the growth rate is worth 10% of the value, then instead if 6.35 the cost per point would by 5.715. Still more expensive then the lvl 81 eng but close enough to be worth paying the premium.
If you forward model the engineers and normalize the engineers raising them all to lvl 103 and giving them same number of vets and experts as the lvl 103 engineer, you will find the lvl 64 engineer will have a slightly higher TA then the lvl 103 engineer that is for sale. So, in the decision making of the purchase, this could be a factor to consider.
Now you have to consider the Time Value of how long it will take to lvl that engineer from lvl 64 to lvl 103.
As I said, this is a basic method, a simple screener, and a starting point for users to take and modify with their own ideas.
However, each user/player must consider what is important to them in making a purchase and play with the numbers.
Thanks again for the input