Amazon has It's Always Sunny in Philadelphia: Seasons 1-4 for $45 with free shipping.
Product Details:
* Actors: Charlie Day, Glenn Howerton, Rob McElhenney, Kaitlin Olson, Danny DeVito
* Format: NTSC
* Studio: 20th Century Fox
* DVD Release Date: September 15, 2009
Amazon.com: It's Always Sunny in Philadelphia: Seasons 1-4: Charlie Day, Glenn Howerton, Rob McElhenney, Kaitlin Olson, Danny DeVito: Movies & TV