For those of you who missed this yesterday, ThredUp extended this through the end of today!
This offer cannot be applied toward shipping, but there is no minimum purchase.
ThredUp has quite a few items priced in the $2-$4 range, so you should be able to get 3 items for around $7 (the cost of shipping).
(Note: Some of the links in this post are my referral links. Read our disclosure policy here.)