Also note that many graduate programs are free*

if you don't count lost wages or the cost of the prerequisite undergrad degree.

But it all depends on what you want, with a fair amount of luck thrown in IMHO. You can have a lousy job with or without a degree, and you can have a great career with or without one.

From ed.gov:

Overall, the median lifetime earnings for all workers are $1.7 million, which is just under $42,000 per year ($20 per hour). Over a 40-year career, those who didn't earn a high school diploma or GED are expected to bring in less than $1 million, which translates into slightly more than $24,000 a year ($11.70 per hour).

*Or rather, funded by your research/TA/etc.