If you have read $40 on this site (or any other) for the RB-Designs modification, it was incorrect.
$165 (US$) includes shipping back to you.
He charges $40 (I think) for a new carb slide.
This may well be incorrect (call mr. ron and ask!), but I think he used to charge $40 to install (incorrect..corrected below) the plate, but that would not include boring the carb, the other modifications (to the jet screen for example) or the jetting changes your carb will come back with.
Again...if you have any question about it, contact Ron. I'll just bet he'll have the correct answers for RB-Design's work!! ;)