Yeah. I'm in the same boat- can't sell a 3.5 mh/s rig for $1500 when it's only making $5-$6 a day.
That is exactly why no one is buying it my friend. A 300 day return of investment is unacceptable in this business
IMHO GPU rigs are better sold for what they are: videogame graphic cards. If you attempt to sell them as rigs you have market @ around 200-300$.