“$35k a year will feel very low to you”
It will feel an awful lot lower once you’ve got used to earning $140K per year and acquired spending habits commensurate with your salary. Conversely the stipend may feel relatively generous if you’ve been living as an undergrad on less than that.
I can’t imagine going back to do a full time PhD after working for a few years. A shorter professional degree perhaps, but not a PhD.