I'm assuming you are at least 40 now, then, because it won't take you more than 4 years, even if you go part-time. $100K is a lot of money. I would look at a few things. First of all, why do you want to do this? If your current career is unsatisfying, and the law intrigues you, then go for it. On the other hand, if you are trying to get rich quick, it won't happen. I had a former student who called me a few years ago thinking about law school because she was worried about her teenaged son's college education, and she wanted a lot of money fast. I had to point out that her son would be almost finished with college before she graduated, let alone paid back her own loans! Let's assume that you are currently working, will continue to work during law school, and you will work for 20 years after getting your law degree. To look at this strictly financially, you would want to know if the difference between what you make now and what you make after graduating would be enough to pay back the cost of law school (plus interest). To be realistic, realize that you won't get a job at one of the high-paying big firms at 45, so you would be looking at lower salaries. If you are currently making minimum wage, then it would be worthwhile. If you are currently making $100K/year, it probably wouldn't.
I will tell you honestly that while I loved law school (I was also 45 when I finished), I would never have done it if I had to pay for it. I knew I wasn't going to change professions, just use the law in my existing one, and I already had two prior graduate degrees, so I couldn't justify paying for another one. It was only because I was working for a university that I was able to do this.