Look at NP salaries, they are very comparable to general practice MD salaries. If you really want anesthesia, CRNAs make well over 100K/yr, and that is 2 years beyond a BSN (Masters level). 50-60K is honestly a bit low for a experienced RN as well.
Also remember that the longer you go to school the more student loans you have to pay off, and even as a MD you do not start out at the top of the pay bracket.