this is fun
Does the AR-15 have a significantly longer distance it can hit targets than a SKS?
Yep. It's not so much an MOA limitation (2~3MOA means reliable hits on frontal torso aspect out to 500m or so, if you take your time) as trajectory: 7.62x39 goes rainbow pretty quickly. Max point blank range on an SKS (using M43-esque ammo) will be about 200m. MPBR on an AR will be about 300m.
Also, the AR's sights are better—this can be largely remedied by spending on better irons for the SKS (Tech Sights, Firesights), siderail scopes, or scout scopes.
$400 can get you an SKS, a scout mount, and a pretty nice optic (Ultradot, a decent ~2x pistol scope, stuff like that).
***
...and if Mr. AR-15 gets you and your three co-targets out in an open space shooting war at farther than 200 yards, he will probably have an AR and four SKS rifles for the price of a single AR.
Well, let's see.
2x SKS: $250
M48A: $150
SVD/SKS standard siderail mount: $50
A nice Dragunov style 6x42 scope: $200
Some nice walkie-talkies: $50
Open field:
You come under massed fire from two widely separated shooters with SKSes. You duck behind a tree. The SKS shooters radio in your position, and the Mauser shooter blasts a chunk of tree through your spinal cord. You die.
Press fire to respawn.
Urban:
You walk into the vicinity of the people's house, apartment, whatever. You walk under the tree in which the sniper is encamped. He radios in your position. You come under massed fire from less than a hundred feet away, with wide angular separation. You die.
Press fire to respawn.
Tactical options get interesting when you start mixing up the weaponry.
Frankly, unless you're really working the "rifle behind every blade of grass" scenario (foreign invasion) in which you will be deployed forward of your own area of residence, more guns (provided they are "combat accurate", reliable, semiautomatic, and quickly reloadable) will probably trump fewer-but-better guns.