Probably out of print and some sellers really gouging on price.

Looks like there are still a few copies of the non-15th anniversary edition floating around for ok prices. That's what I have, I assume they are the same?

https://www.amazon.com/Farscape-Complete-Blu-ray-Ben-Browder/dp/B005CXOG8M/ref=tmm_mfc_swatch_0?_encoding=UTF8&qid=&sr=

edit: It also looks like you can buy 15th anniversary stuff per season for 34-50 a season.
https://www.amazon.com/Farscape-Season-1-Blu-ray/dp/B00F6WXPR2/ref=tmm_blu_title_1?_encoding=UTF8&qid=1497444364&sr=1-2
https://www.amazon.com/Farscape-Season-15th-Anniversary-Blu-ray/dp/B00GHH9HQ8/ref=pd_sim_74_1?_encoding=UTF8&pd_rd_i=B00GHH9HQ8&pd_rd_r=FA1VTMCJBE8KP4TD0TJV&pd_rd_w=de1Xo&pd_rd_wg=Su80m&psc=1&refRID=FA1VTMCJBE8KP4TD0TJV
https://www.amazon.com/Farscape-Season-15th-Anniversary-Blu-ray/dp/B00GOT16D6/ref=pd_sim_74_2?_encoding=UTF8&pd_rd_i=B00GOT16D6&pd_rd_r=FA1VTMCJBE8KP4TD0TJV&pd_rd_w=de1Xo&pd_rd_wg=Su80m&psc=1&refRID=FA1VTMCJBE8KP4TD0TJV
https://www.amazon.com/Farscape-Season-15th-Anniversary-Blu-Ray/dp/B00GOT13M0/ref=pd_sim_74_3?_encoding=UTF8&pd_rd_i=B00GOT13M0&pd_rd_r=FA1VTMCJBE8KP4TD0TJV&pd_rd_w=de1Xo&pd_rd_wg=Su80m&psc=1&refRID=FA1VTMCJBE8KP4TD0TJV