It is really nice to see that you are honest about your concerns as well as aware of the reality that financials whether we like it or not are something that we should be taking into account when making decisions. So there are pros and cons of any of the four choices that you outlined and you will lose something by choosing any of the four options. I graduated college May 2017 and was mulling going to go to law school, instead I decided to go into a consulting and work for a few years. I still plan on doing law school, but in a few years for certain. Choosing to work a job right after college can be great, but be aware that it can be difficult for some people to go back to school after having made some money; to go from making a salary to being a student and largely having no income source is difficult for some people. The money can be intoxicating and going back to school is not something that some are willing to do.
So medical school is without a doubt expensive and many are unable to afford it and take out loans. If you choose to go to med school know that you are not alone in having taken out student loans and that there are many others just like you. Going to medical school can lead to a great career, but you must be aware about the reality of the situation; you will likely incur a good about of student loan debt and be in school for years. This is not to scare you, I just want to be honest with you. You will have to pay back your loans and that amount varies greatly from person to person depending on how much they have taken out and the interest rate. It may take you a few years or a decade; there are friends of my parents who are still paying back student loan debt from when they went to law school and it has been 15 years. BUT, a career as a doctor can be very lucrative so you may be able to pay back loans in short order. If you want to be a doctor then you definitely should look into med school but you should be honest with yourself about the cost and truly reflect on the level of debt that you are willing to take on.
So a PhD program is a great option but leads to a very different career than going to med school. The stipend is nice and all, but by no means are you swimming in cash. I have friends who are pursuing their PhDs in economics and it's not like they are living the high life; they are able to survive on the stipend but its not a cushy life. Pursue this path not because of the stipend but because you actually want to; by choosing a PhD program are you doing so because you want to pursue this line of work? Don't do it for the cost saving, do it because you're interested in this career line.
All in all, finances are an important part for sure but they aren't the only factor you should entertain. Also be sure to weigh your interests, if you want to start your career after graduating don't pursue a PhD because you're afraid that the money will be intoxicating. Follow your interests while also weighing the financial cost, interest and costs are not mutually exclusive.
I hope this helps and I wish you the best of luck!!