I'd be willing to bet that within the next year, you'll see a new TRE/HL edition from Polaris with the same gearing in an RS-1 setup, so it may be an option at some point in the near future....but until then, the billet case with upgraded internals are the only way to do it really, if you have a donor diff, then it would be around $15-1700, which isn't relatively terrible, but if you don't, the gears and output hubs are what makes the price shoot up, since you'd be looking at basically buying a complete diff from Polaris to get them, around $1200. You can buy the gears and hubs individually...but the prices they have on them are almost the same as buying a complete new diff.SATV billet case built with HD parts and TRE gears would be very expensive. I would want to assemble it with tight tolerances using shims and I don't know where you could buy them or if they are available?
If SATV can put that parts list together with a price I could live with for years of reliable service I would consider it to be the best option.
The two things I feel are the weak links in drive line components are the front diff and driveshafts. Axles are close 3rd, but solution exist for that.