I actually just completed a very similar trip to yours, except in reverse. I started in Chile and went north to Inuvik! Loved the Dempster Hwy!
You are in for a fantastic experience. Good luck to you although you sound like a fairly experienced rider who knows what he's doing, you should do fine.
Yeah, keeping to that budget is tough. Fuel and tyres were far and away the biggest expense of my trip. Plenty of free camping in the States, I loved National Forest land, so much beautiful empty space to roam, camp, ride, do whatever.
I'll keep an eye on this thread, as I said you seem to have it fairly well figured out, but if you have any questions or want some advice feel free to ask.
Oh, and I did it on a Tenere too! But the single cyl 660cc version.