I'd personally go for the ranged gig -- on a budget, toss on an ACOG, but have an AP (unless it's an RDS ACOG copy), perhaps camo paint it, and then spend a wee bit more money on at least one good, bright flashlight (G&P?)
If you want to go the cheap route to an M203, the Marui will work, well with an RAS, and still look rather nice with an ACOG or RDS on top -- a VERY useful assault setup on a tight budget would be:
TM M203 for M4
ActionHorn ACOG RDS
A 65 Lumen TacLight (Big5 even has a nice S&W one) -- SwatForce Xenon works, or for a bit more dough, G&P makes awesome surefire replicas. OR, you could get a Surefire G2 or 6P, and have a light that'll outlast your gun.