With orders of $25 or more, Amazon offers the Verbatim Slimline Wired USB Keyboard for $4.95 $4.69 with free shipping. (Newegg Business charges the same.) That's the lowest price we could find by $8. It features function keys and a full numeric keypad. It's compatible with Mac and PC.

Note: This is part of the Amazon "add-on" program and can only be purchased with orders of $25 or more.