Round trip plane ticket to Canada: less than $200
Price of an abortion: $200 - $300
Total price: $400 to $500 and they can put it on their credit card. It's even cheaper if they take a bus to Canada. For a women facing thousands of dollars in prenatal care and thousands to raise the child this is pocket change.
Most women in this situation will never make the financial analysis you do. The immediate cost is all that matters. In that case, the adoption route will be the cheapest route.