Right now, 93 is at $3.25/gal. It's been fluctuating between $3.15 and $3.55 since I've owned the truck.
The higher elevation you are, the lower octane requirement, because there are not at many O2 molecules being crammed into the cylinder at any given time, boosted or not. 91 octane would be plenty for you rickashay, and 89 would probably be fine at elevations above 7k feet.
And no, I've never put a calculator to it to figure out exactly how much more or less i'm spending paying for premium gas, but getting decent MPG because of the blower. I consistently get 250 miles on 15 gallons of gas. Corrected for tire size, that's ~17mpg average....and 75% of that 17mpg driving is in town, stop and go, idling, etc. At $3.25/gal, each fillup is basically $50.
300kilometers a tank is only what, 180-190 miles? Ouch. With how much I have to drive, I've be forced into a car if I was only getting that. WHich is the main reason I didn't lift it, and put 33's and armor on it. Sadly.