Now that you have decided to go the Mac route, consider not buying the iMac. Take a look at one of the Mac Books and using a monitor for the screen. I've had iMacs for 10-12 years, still have one. Once I bought a monitor ($80-$100) to use with the Mac Book Pro I don't think I have turned the...
At 15,000 miles/yr, my difference between $3.80 and $5 a gallon would be $55/mo (27 mpg). I'd still drive where I want to go, when I want to go without a second thought. Like many others, I'd just cut back on the higher gas costs by not buying $55 a month in stuff I probably didn't need anyway.