PhD

I have electronics and digital design/verification background (MSc and some industry experience). As in the title, I am interested in learning and lately I got particularly interested in formal verification and started reading books, watching tutorials, on top of applying it at work. I really would like to learn more, participate to its advancement and contribute even slightest. I also enjoy academic environment. This is why I am considering a PhD. However leaving my job for full-time PhD means significant paycut even if I get into a funded PhD, also I am here on visa and many programs require you to pay the difference between foreign student price and domestic student price out of your packet, after receiving the funding. So leaving my job is likely not an option. I thought about doing a PhD part-time on top of my job. It will be very time and energy consuming, but I think I can take that. My bigger concern is, part-time PhD will take long time (6-8 years) and field is ever-changing, I am afraid my thesis may become irrelevant by the time I finish it. Also what I hear is that, if you do it part-time, you will not get the best subjects since professors would like to provide better supervision to and quick return from a full-time student. So I am hesitant about a PhD, even though it was something I was thinking of since a very young age. What do you think about a PhD, do you have any advice, some opportunity or downside which I did not consider? And if not with a PhD, how do I learn and research more? Reading and taking online courses are always options, but the problem is without any supervision, clear goal and guidance, I am sure I will get sidetracked and it may not be very fruitful.