A tax on abortions would be effective only up to the cost of leaving the country and getting the abortion in another country.\
You can only prevent poor people from getting abortion with laws and/or money,unless you enforce travel restrictions on pregnant women. People who can travel, will do so, just as they are traveling now to combine safari vacations with nosejobs in the RSA.
Plastic surgery, knee replacement, heart transplants, dental implants are all state of the art and far cheaper than in the US.
If you tax abortions too much, the pregnant woman who can afford it will simply hop on a plane and fly away to get it done elsewhere. Restrictions can only be on the poor who cannot afford to leave and the ignorant, who are not aware of leaving the country. You cannot prosecute someone for having an offshore abortion unless you can prove she was pregnant, and we do not check women to see this when they leave. I imagine that it would be unconstitutional to do so.