Newegg offers the refurbished Logitech MK520 Wireless Desktop Keyboard and Mouse Combo, model no. 920-002553, for $19.99. Apply coupon code "VISACHECKOUT" and check out via Visa Checkout to cut the price to $17.99. With free shipping, that's $5 under our February mention of a refurb and the the lowest price we've seen. (It's also the best deal we could find for a refurb today by $7.) This mouse and keyboard set features an ergonomic design, 2.4GHz wireless connectivity, and more. It purports to have up to three years of battery life for the keyboard and one year for the mouse. Deal ends October 1.
Note: A 90-day warranty applies, but it's unclear who backs it.