Michael's Craft Store & Hobby Lobby has really cheap red shirts you can buy. (I suggest saving those 40% coupons from the paper, so you can spend even less)
And out of a HR suggestions, I went to Goodwill and found multiple Target Polo's for $2 a shirt.
Bullseye Shop has really good quality shirts, I will admit, However, if your working part time, and maybe looking for other jobs, why pay for the shirts?