Delta is the same price for one as it is for a case, the killer is shipping on one item, so I always order extra shirts, sweatshirts, hoodies etc.
They have a lot of different weights of shirts, I always use their 6.1oz "Platinum" and for a white adult s - xl it is about $1.06 (2x and above to 5x 2.40) colors go to 1.72 and 3.05 for 2XL and above.
I just ordered their Platinum Longsleeve in colors they run a bit more, white 1.85 to 3.40 and colors 2.05 to 3.75 based on sizes.
The garments are nice weights and with the different weights they sell you can fiund almost everything you need.