I just got back from a 3,000 mile trip, and, yes, the price of fuel hurts (especially diesel right now!), but it was only a few hundred more than if the diesel prices were $1 or $2 less per gallon, and since that's way less than the price of staying in a hotel every night of the trip, it is still worth it.
But, yes, I did figure in the cost of gas for the first time, before this trip.
Probably the bigger change for me has been looking for used small vehicles that I can pick up cheap for around-town driving, rather than using the truck as a daily driver. It makes no sense to drive to work in a truck when I could be driving a motorcycle or small car.
As far as the 85 octane gas, that's a historic carry over - counties in the US with altitudes above a certain level for most of the county can reduce the octane in the gas they sell (which makes it burn easier and thus knock more - the higher the octane, the harder it is to ignite the fuel vapor), either by 1 or 2 points. The logic is that with thiner air, there is less chance of knocking due to a richer mixture, so it isn't a major issue for cars. That was true for carborated cars (which was pretty much all you could get when the law was passed). I've heard mixed reports about it for fuel-injected cars (I've never had a car have a knocking problem at this altitude, even when using 85 octane gas - but of course I could have had a car that was simply masking the knocking by it's computer adjusting the mixture in response to feedback from the knock sensors, in which case I lost a bit of performance), and think the feds probably need to re-study that particular law...