This survey started in 2010 and got updated recently with 22,000 owners of AR and AK platforms surveyed.
Most MSRs were...
...purchased from an independent retail store
...average cost was $1058, down $25 on average from previous year
...in .223/5.56mm for ARs, 7.62x39mm for AKs
35% of respondents had some military or law enforcement background, down from 44% in 2010
49% purchased their first in 2012 or 2013, of which 82% were ARs
Spent $211 to $381 in accessories
92% used for target shooting, 50% for hunting, 19% for competition.
There is a few more information you can read from the Shooting Wire
From: The Shooting Wire