One last thing is, while in straight up dollars and cents you may not come out ahead, this is true.
On the other hand, you do have complete control of the process, how ever messy it may be.
Cutting the grain where and how you want, sizing pieces for your needs, etc. This is the stuff that's hard to calculate. When you buy wood, most times, you're at their mercy.
Doing it all yourself, you can cut, keep and pitch what you want to.
Firewood is a bonus