Sell the SUV today. Buy the Ford Focus in OR tomorrow - and pay the $0 sales tax.
Drive it across country when the time comes - and be sure to get chains. Sure, you'll have to license it in OR, and then again in IL, but that cost will likely be less than paying the IL use tax. IMHO...
Probably this.
Although...it might take 2 days back and forth but I'd first internet shop that car in IL.
DON'T PUT YOUR PHONE NUMBER in the query: and I'd open a yahoo or free account so it's not your main email as car dealers will spam you for years.
But if you're only talking a grand difference...it's theoretically possible with hard negotiating to make that up. One reason is different states have different cash back rebates and even finance rates. Also, check seriously at end of the month and especially end of the year: if it's on their lot, they want to move it at that time the most.
I used to live in Oregon...isn't there a 5 year option for registration?
Depending upon how big a town you move to, and how strict they are...I'd just drive with the out of state plates until I was past any additional taxation period. If stopped I'd say, "Sorry: I'm moving back because xyz (not enough cabana boys to play with, serious lack of mountains, poor selection in stand up comedy clubs....whatever).
Most cops will laugh and let it slide one time. YMMV. Although if IL was a second home...it would be legit to keep the OR plate.