Ordering from the UK

Does anyone happen to know what shipping would run if I ordered some t-shirts from the United Kingdom? I heard there's no customs duty on orders under $50, so if I can snag a decent deal online, it might actually be worth it... my only real hang-up is figuring out how much they'll charge just to ship one or two shirts over here.

The seller is the one who sets the shipping rates, so you should probably check the fine print on whatever site you're planning to use before you pull the trigger.
Just speaking generally here, since I've done this quite a bit when ordering perfumes—shipping can be as low as $3 if someone just slips a few small vials into a padded envelope, but once you start ordering from a major online retailer, you're looking at closer to $6, or honestly even more depending on how heavy the package is...

~3 to 4 pounds, give or take... It’s relatively light packaging, not particularly heavy, and since it isn't fragile, there's no need for any specialized padding or extra care... so, I suspect the cost won't be much more than that.