Pricing is the right approach, although using percentages to alter pricing is risky because you run the risk of "A10" workers being paid even less in nominal terms so that they're still cheaper WITH the added taxation.
I think with a lot of the outsourcing mills that are foreign-owned, you might end up seeing complex compensation systems that involve fractional payment deferred or paid into accounts overseas so that the nominal wage remains competitive even with additional marginal taxes.
I would tweak your plan slightly:
1) H1B workers must be paid 125% of the job's regional maximum
2) H1B workers must be employed and paid directly for the business who is the end beneficiary of their work -- they may not perform any contractual labor
3) H1B workers are fee to switch employers during the term of their visa
4) Violation of these terms is a crime. Employers are subject to a fine of 3x the employee's annual salary and a 5 year ban on hiring any H1B workers. H1B workers are subject to immediate detention and deportation for violating these rules. Employers who violate these terms for more than 1 employee concurrently are subject to criminal prosecution.
(1) Insures they are no longer cheap labor and business-critical innovation geniuses will make this kind of salary anyway.
(2) Prevents them from being used in labor mills or enabling foreign-owned firms from side-channel payments. They must be direct hires.
(3) No indentured servitude. This prevents businesses willing to accept higher salaries but who set extreme working conditions to cost-average their output to local salary levels ($/hr).
(4) Puts teeth into enforcement.