Semi auto? dunno
If it's F/A say $3000-ish give or take depending on condition?? ...if it is full auto then I think subguns had a few Cobray M11s on there last week in the $3200 range unused in the box...prices go up from there with suppressors, lots of extra mags, etc.
Keep in mind those are only asking prices...who knows what they actually go for.