I've recently found a (Swiss) shop which has the main business of printing and stitching logos onto bulk shirts, but will happily sell me low volumes of the blank clothes as well.

Those do typically have shit quality at bargain prices, but as soon as you pay more than, let's say 10 EUR for a simple shirt, the quality is quite good (certainly better than C&A or most branded merch).

That might be an avenue worth investigating for you as well!