I believe estradiol has a half life of around a day when taken sublingually, two days when swallowed. After this time a sufficient level of estrogen will not be in your body unless you take more estradiol. The same goes with spironolactone, after you stop taking it and its half life expires your testosterone will no longer be blocked and will rise eventually to its natural levels.
Males transitioning into females of course need to stay on estrogen their entire lives, as do females transitioning into males need to stay on testosterone for the rest of their lives. The male endocrine system doesn't naturally produce the amount of estrogen females naturally have, and visa versa. The only exception is when someone undergoes SRS there's no need for Spironolactone anymore since there's no testosterone to block.
Finances shouldn't be an issue. Most all hospitals offer 'free-care' which allows patients who don't have either private or state insurance to get medical coverage for whatever they need. With that you could get proper oversight on your HRT treatment where all of this should have been explained to you.
Like in my previous post, HRT should be a permanent treatment. Transitioning to a certain point and then stopping doesn't work. Say if you have breast development, then stop, like painter said above that will go away as the maintenance of your development is just as important as the start of it. If a male lost his testosterone he'd get lazy, lose muscle mass, become unmotivated, etc. If a female lost her estrogen she'd be a mess. Only being prescribed 30-days worth of hormones, then checking in is inappropriate in my opinion. HRT is not like trying sleeping, or anxiety medications, where you try them for a week or two, see if it makes a difference, and continue or stop. My endocrinologist wrote my first script for 6 months, and then a year's worth ever since I started with 6 month check-ups.