I have a 22" rifle gassed Black Hole barrel with 1:10" in 204Ruger AR, it's their "national match" profile so it's heavy under the handguard, but 0.750" gas block. It's rather well balanced with a 15" Troy Alpha rail and JP low profile gas block. I did some digging before I ordered my barrel, I went with the 1:10" because I wanted to be able to run the 40grn pills comfortably, maybe even up to the 55's.
The 204R is the assembled rifle, the 18" lone upper is a 6.8SPC.
Without optics, no charging handle, no BCG, there's a touch over $650 in that 204R upper. I spent a bit of extra money on an adjustable low profile gas block, and a bit extra on the handguard, otherwise, it's a $50 overstocked stripped upper and DPMS upper parts. The BHW barrel was just under $300 itself. I'm hard pressed to buy anything used, so for $500, I'd just build my own. If you consider that I could have saved $30 on a cheaper gas block, $50 on a cheaper handguard, and maybe $50-100 on a cheaper barrel, then you'd end up less than that $500 for a NEW upper, not a used one.
My experience so far with the 204R is that it does NOT wear on barrels like the 22-250 or 220swift. Even with those two, unless you're shooting colony varmints, the barrel life is quite good. Comparatively, the 204R runs a lot less powder than either of those large case 22cals. It's a smaller bore diameter too, and still high pressure, but it just doesn't seem to have picked up any reputation as a barrel burner, and my experience agrees with that.