Right now on eBay
Uncanny X-Men #510
Marvel Comics, July 2009.Rare
This partial sketch variant seems to have been given out selectively in 2009 at both the Heroes Con in Charlotte (North Carolina) in June and the San Diego Comic Con (California) in July.
The variant is a partial sketch (Psylocke is in color and the background is sketched) version of the J. Scott Campbell retailer incentive cover (below), hence is a variant of a variant!
The partial sketch variant does seem quite rare and hard to find on auction sites; also only 15 have been graded by CGC in early September 2015 (2 more than in September 2014).
Although sales are few, these seem to keep rising in price: in 2013 a CGC 9.8 sold for $725, a year later a CGC 9.4 NM copy sold for $1,000 and another year later, in Summer 2015, a different CGC 9.4 sold for $1,351.51 on ebay.