Floter, I don't know what crappy AR you have but every Ar I've ever shot has been a great gun.
Now back to topic:
A Muzzle Brake on a .22 Rifle.
A KAC Silencer on a .22 Rifle.
Hundreds of Dollars worth of alterations to a $179 SKS.
Barrel Extensions.
Faux Flash Supressors. Look Cool, but are useless.
Scopes for AKs, ARs, etc.
Armscor MAK-22s. They are cheaper than regular AKs, but run about the same as a MISR-10. Considering they come with 10 Rounders, I'd rather have a MSIR for the price.
MISR Single Stack Mags.
Kits to convert a perfectly good 30 Rounder to a PC 10 Rounder.
Any Non Semi-Auto. shotgun over $300.
Shotgun attachment fro AR-15. Not for usefullness, but for charging $2000 for a $200 Shotgun with the stock removed and barrel cut to 10".
12 Gauge Bird Bombs. They were meant to be 37mm. Don't put them in shotguns.
Less than lethal ammunition.