This is how I fixed mine when it happened to me. I didn’t realize the AC was using the same air filter as my furnace, so it had gotten really dirty and blocked airflow. A cheap new air filter replacement fixed all the issues.

Chain thrift stores aren’t anywhere near what they used to be. Goodwill’s been crap for awhile, but now I’m even noticing Salvation Army’s being pretty expensive. The best places to go are always the hole-in-the-wall local thrift stores that aren’t part of some larger chain - that’s where you can find great deals. Unfortunately, those also tend to be small places with low selection, so I rarely go thrift shopping for a specific thing, since I’m not likely to find exactly what I’m looking for on any given trip. The the kinds of people who are able to find a bread maker for $8 are the ones who frequent a bunch of local thrift stores just for fun, buying stuff they want as they happen to find it.