As someone who has ordered screen printed items in the past, I know a little bit about this.
To start, the more items you order, the cheaper each item is. similarly, the fewer items you order, the more expensive. Hence the dozen minimum order. This has to do with creating the screen (which can be pricey for one item), as well as setup expenses. So unless you find a company that has a stockpile of jobshirts with PARAMEDIC screened, or an order about to be placed, it will be expensive. Ditto with embroidery, but your more likely to find a place to do a single item (but they are generally more expensive anyway, so it doesn't appear to have that much of a markup).
good luck finding it, but I don't think you will have much luck for a custom single item for cheap.