Update: This very popular deal is still available.
Store4PC via Amazon
has Sabrent USB Bluetooth 4.0 LE Micro Adapter
(BT-UB40) for PC for $3.77
w/ promo code 46EMDR3K
. Shipping is free
w/ Prime or on orders $25+. Thanks iconian
Note, promo codes are typically limited to one per account. Works with Windows 7 and up. Low Energy (LE) feature only supported on Windows 8 and up.