Moving ahead with education

Just having finished a second masters degree in the spring, my thinking is moving on to a Ph.D. But oh, the cost. Why does it cost so much to get a degree? Starting as late as I did to go back to school, now the question is how reasonable is it to start on another degree and spend all that money when I am pushing 64 in January? But it is so delightful to go to school and continue learning!