These are not $800, but I just to post... SxS gun porn
http://www.gunsamerica.com/Search.aspx?T=purdey
With your budget I'd look for used-in-new condition guns from Franchi, the Ruger Gold, Fox Savage, SKB, Miroku, Huglu, Dehaan. It is gonna be tough to get a newer SxS in that price range, but you may be able to get an older one in good condition.
http://www.gunsamerica.com/Search.aspx?T=dehaan
http://www.gunsamerica.com/Search.aspx?T=fox%20savage
Oh yeah, I just remembered that CDNN has been selling new Charles Day filed model SxS for very reasonable prices, less than $500!
http://www.cdnninvestments.com/