If he used the Oracal 631, there is no doubt he could have bought the vinyl for $120, as claimed. Just a quick look online and I found SignWarehouse.com sells if for .38 per sqft, making 300 sqft $114. Was it made for this use, not a chance, but, this kid made it work, and frankly, the job looks pretty good from the pictures.
The bottom line is that he was willing to put in the time (8 days), and doesn't put a value on his time (none of us do when doing a DIY project). The better question for the kid is, how much would you charge to do this job? Are you willing to work for free?
Much of what we do as sign guys/gals is priced on "perceived value", as well as a full costing on materials, labor, shop expenses, etc. We can't expect a DIYer to consider those things.