If it's not ethical to buy a t-shirt for $5, it's possibly not ethical to buy it at any higher price either - easy enough for a retailer to sell the same $5 shirt at a higher price. There isn't really a structure which allows me to know by inspecting a shirt what was involved in its overseas production.

You can thank the media for contributing to this too. Constant stoking of greed and vanity and materialism leading to an endless cycle of throwaway consumerism.