That's a rather high price from the plumber's supply, you might check
around. When I was shopping for 3/4" pipe for clamps, I looked at the
Borg vs Plumbers Supply and encountered a similar problem with the
threading: the Borg threaded for free, but charged over $10 for 10'
sections; the Plumbers Supply charged only $7 for 21' sections. They
would thread, but really didn't want to and charged something like $5
I learned from the pro shop that (at least here in TN) they sell only
21' sections, and most all their clients have their own threaders, so
their policy makes sense.
My solution was to buy a cheap threading set (Homier sells one for $20
that has 4 sizes and works fine) and save on the pipe by buying 21'
sections at the pro shop. It was a good investment and I've used that
threading set several times since.
Something to consider for next time...?