I don't think it's that simple. That formula is too black and white. What's valuable for one could be worthless to another at any cost. Also, there's more than just monetary cost. I think a better equation is value=perceived benefit/perceived or actual cost.
The intent was to point out some of the absurdity of an endless search for "value".
My experience with group lessons was rather different to yours. For whatever reason - luck with instructors or more easily satisfied or working it harder - I've had plenty of improvements from group lessons. Mostly in BC Canada but not always. And I've continued down the path by doing instructor courses. It's all been great value.
Previously posted my thoughts on how to get the most out of a group lesson but here's the highlights:
1. Do a little research on instructors - that may mean taking some lessons to find the right ones to work with.
2. Turn up prepared. Warmed up ready to ski and able to answer the question: what do you want out of this lesson?
3. Participate: Ask questions; take the opportunities to ski right behind the instructor without monopolising it); work it through the lesson.
4. Make notes either during or immediately after.
5. Practice what was taught and learnt. Probably the biggest thing is not to immediately over-terrain after the lesson. See it all the time - people who have begun to acquire new movement patterns in a morning lesson immediately head for the gnarly terrain and immediately go back to their old ways. And then wonder why the lesson didn't work and their instructor is talking about the same thing next time.
The bit about the unbuckled boots 1st run implies to me that you are probably a go for it sort of character. That's great but it needs patience to ingrain new movement patterns. Learn on the green and test on the mean. Which may mean spending a lot of time on the green and blue.
There's a similar situation in golf. The driver is longest club in the bag and therefore the most difficult to operate. We lose form very quickly with that club. Yet down the driving range there's people hitting ball after ball with a driver in a misguided attempt at mastery. (It's not even the way a round of golf is played.) Far better to use a short iron to build form then hit a ball with the driver and then back to the short iron.