I'm kind of in the same boat as you. Though they are expensive, my favorite tees are Alternative Apparel. They cost about $10 a piece for the ones I like, but I am figuring that into my end product's final price.
I'm also looking at https://www.royalapparel.net
and "Bella" has some American made. There is also Loomstate, but I am not sure yet what their wholesale prices are. They may be really out of my price range.