Hard to call it a monopoly when there are literally (3) different 5-speed transaxles from (3) different manufactures to choose from.
An Albins 10" 5-speed sequential is $33k.
https://weddleindustries.com/products/AGB10-SS5-TRANS/AGB10-SS5-TRANS
A Fortin 10" 5-speed sequential is "Call for Pricing". Last I heard, they were north of $35k as well.
https://www.fortinracing.com/product/frs5-sequential/
Both of these are equivalent to the 10" S5 transaxle priced at $17,500.
https://weddleindustries.com/products/S5-TRANS/S5-TRANS
A S4/S5 R&P is about 1/2 the price of the Albins and Fortin R&P sets when it's time to replace.
I have a PBS with a split main case to convert to a Weddle S5 on my bench now, I'll head back downstairs and get to work.