Amazon is currently having a sale on three MST3K boxsets: The 20th anniversary, volume 17, and volume 18.
All sets have a MSRP of $60 and are on sale for $26.
The 20th Anniversary set (volume 13) contains First Spaceship on Venus, Laserblast, Werewolf, and Future War. (Link)
Volume 17 (XVII) contains The Crawling Eye, The Beatniks, The Final Sacrfice, and Blood Waters of Dr. Z. (Link)
Volume 18 (XVIII) has Lost Continent, Crash of the Moons, The Beast of Yucca Flats, and Jack Frost. (Link)
I don't know how long this sale will go on, so get them while you can!