I'd say 5.7K for an 11/9 is fantastic right now. In terms of demand, I see M11/9 as the more desirable, at least 3 times the amount of people I speak with want them over 11A1s or 10s.
Condition, how they run, and who has them all have a bit to do with price.
I would support paying a bit more for someone who has it safe and secure, and is trustworthy. Condition could be huge, if the holes are egged and it is either full auto only or has some sort of feeding issues it could be an easy solution or it could be a headache. If it's a reputable dealer, you can generally rest assured it will sit in a safe and be taken care of with love. (Condition at sale and transfer will remain the same.)
If it's from Jimmy Smith in Someplace City, USA and you have just seen so-so pictures... who knows you could pay the money and he could abuse the heck out of it before transfer. Welds could be breaking, feed ramps could be screwed, holes egged out, etc. Kind of like buying a car... if you go to a high end dealer you will pay more but you can get a better idea on history. If you buy from some guy down the street, there's always some question about where it's been.