You can avoid becoming resistant to the medication by taking "holidays". I usually do this Friday-Sunday most weeks. A daily alternative can be wellbutrin or aplenzin as well.
Also most people can get away with generics so even without insurance the meds are cheap. The psych visits will cost $300-400 a pop though....
Most of these are still schedule 1s though, so if an insurance change forces you to a new GP you can get the prescription yanked - there's no guarantee of access to methylphenidate in the US, there aren't any over the counter methylphenidates and any other acquisition route would probably break the law (like buying it in Mexico or from a friend).
That said, at some point it's going to be worth it to just pay out-of-pocket for five minutes of your old GP's time to write a new script if things are dire... but the fact that this barrier can exist is troubling to me since being in that ADHD hole makes it so much easier to get over these barriers.
For some folks wellbutrin/bupropion can be used to treat ADHD. It is schedule IV so access is easy and generics (I think generics kinda suck for me with this med) are very cheap. Does it work as good as stimulants? Nope, but its certainly easier to get and can help some people.
I feel going to a GP to get a very restricted stimulant is a uphill battle. Go to a ADHD specialist psych. Despite having diagnosed ADHD since I was ~6, my GP looked at me like I was crazy when I explored getting back on meds. I went to see a specialist instead.
My personal experience here is a bit limited - I grew up in the states but after college I emigrated up to Canada so... yea I generally get scripts from my gp up here for a full year's supply at a time and end up paying something like 1/30th of a cent (CAD) per pill for it. While I was in the states I had to fight to keep my script when I transitioned from my parent's insurance to my employer's in college, and ended up paying 9$/pill for a few months but I accessibility was always maintainable without ever seeing a psych except for initial diagnosis in middle school.
My experience with US ADHD medical providers is that they require an appointment every 3 months where you get another 3 scripts (with 2 being dated for the future months). One let me go a whole year without having an appointment but I also didn't ask for a script every month. Generics stimulants have been cheap with and without insurance (or with GoodRX).
After I moved and got a new GP and asked for a stimulant prescription, they wanted me to come in every single month and do a urine drug screen even if I provided info from my former providers. I switched to an ADHD specialist right after that. It's much more expensive but they treat me with respect.
Yeah I have to go in monthly to get mine as well. Thanks to college kid abuse and the opiate crisis doctors cover their ass when it comes to writing stimulant scripts. This means monthly visits (and they get $300 each time) and sometimes drug tests.
Also most people can get away with generics so even without insurance the meds are cheap. The psych visits will cost $300-400 a pop though....