Some cost many thousands more than $1500.
I should probably be buying several dozen S&W M&P 15-22 .22 long rifle guns right now. They cost just a few hundred dollars. I could make a killing when the government starts paying me $1500 a pop.
Would you stop with ARs? What about the AK-47? SKS variants?
Since you are banning a type of rifle because it looks bad ass (and so mass murderers are attracted to it), would you also ban red, pink, gray or green ARs? They do exist. What about wood stock AR's? They also exist. As far as I know, no mass shooter has ever selected a colored AR or a wood stocked AR for a mass shooting. Why ban those as well?
What about guns like the Ruger Mini-14 (pictured below), which shoots the same bullets at the same rate of fire?...but is never used by mass shooters? Are you ok with that gun? Or, would you ban it as well?