You could probably get in with $4k if going for a lower grade PVS-14 but if you're actually wearing it for any duration, you'll want to spend the extra money on a quality helmet, either Ops Core or Team Wendy plus a Wilcox mount.
I've got the Ops Core FAST ballistic and bump helmets; if I had to do it over again I probably would've gone with Team Wendy since the bump helmet has an aluminum insert instead of just the plastic molding on the Ops Core bump helmet.
I've had positive experience with Larry at
www.ownthenight.com