IRG imports the Nodak aluminum lower (
http://www.nodakspud.com/NDS-18S.htm) for the RWA 180B upper. Both are compatible with the original 180B parts.
Back when Canada Ammo was working on a 180B lower I tried to get them and RWA together but unfortunately either timing or pricing sent RWA to IRG.
The 180C was designed from day one to be $1000, they sacrificed in areas to get and keep the price there, that is why the prices are so different. You are not buying the same rifle and the quality is not the same. It sounds like they were still able to produce a decent rifle while keeping to the original budget but there have been a few reports of issues (just like any new product to market).
I prefer the Kodiak/Wolverine version simply because Wolverine is involved. I will not deal with IRG and since I already own an original 180B I have no use for the RWA upper.
Calgary Shooting Center is carrying RWA AR180 parts but last time I was there the "kit" they had was pretty much everything needed to complete the Nodak stripped lower which I did not need. I'm hoping they start retailing all parts.
RWA also mentioned at one time that they would be making custom gas system parts so hopefully those come soon so guys can start swapping barrels more easily on the 180C (harder to find 18.5+ inch barrels with carbine length gas).