If I had to guess at the reason for the price difference, it's probably in this part of the stats:
Std. Upgrades/Accessories: Advanced safety, bipod, imaging
scope (thermographic, image link), metahuman customizations
The Barrett doesn't come with an imaging scope of any sort or metahuman customization, and doesn't have an integral gas-vent (mentioned in the description). But the Barrett does have an integral silencer and smartlink. On the whole, I'd probably rather have the Barrett, since I can add the accessories I'd want easily enough, but the Minotaur comes ready for a troll to use straight out of the box.
By the way, the stat block neglects to note that the RC would increase to 4 with the bipod deployed. Should be listed as "2(4)". ....Not that that matters with a single shot weapon. And why is this single shot? The picture looks like a semi-auto weapon to me.
Yeah, in retrospect, the Minotaur is a bit goofy. It's also listed as an "anti-material" rifle instead of "anti-materiel". "Material" is what you make clothes out of. "Materiel" is military hardware.
As for whether the damage and AP are right for anti-materiel rifles... well, there's the rub. The SR game system has never really acknowledged just how substantial the difference in armor penetration is between hanguns and rifles. It's something that we just have to put up with. It's got way more AP than most man-portable weapons in the game, so by comparison it is anti-materiel. And you have to combine the damage and AP to get the true anti-armor potential: armor less than 14 is useless against these rifles. (Most of the light-armored vehicles in MilSpecTech have about a 14 armor.) Throw in anti-vehicular or anti-tank ammo and you're got another -6 AP. That's enough to beat the armor on a Citymaster APC at least. Called shot for +4 damage to be sure, and most of the LAVs will at least feel it, even if they're not instantly crippled. True, it won't do much against a Main Battle Tank without lots of successes, but MBT armor has long since left the .50 BMG round in the dust even in the modern day.