What do you need to look for? What is the cheapest plane to operate? Not a c172 but a plane with a little more horsepower? What would be an hourly cost to operate this plane and how do you calculate this? Like fuel, maintenance, etc?
You've gotten plenty of advice in other threads in terms of what to buy... DA40, Bo/Mooney, Twin Comanche, etc. depending on your goals.
There's no such thing as a plane that's cheap to operate... Just differing levels of expensive!
I've paid the bills for several airplanes, and I doubt you'll find anything that costs less than $40/hr in maintenance. To get that figure, a newer airplane would be a plus - I think we're pretty close to that with the Mooney ('97) and Diamond (2006). For a normal 1970's fixed-gear spam can, $50/hr is closer to the mark. If you're buying something older yet and/or with two fans, probably $60/hr is a good initial budget number.
Keep in mind that none of this is going to hold true in the short term. You'll have times where the plane will be humming along great for months with very little expense, maybe even years without anything major, and then you'll get hit with a $15,000 bill for fuel cells or a $35,000 engine replacement. It's important to be ready for that.
As far as costs go, the ones you have the most direct control over are fuel and purchase price. Buy a reasonably-priced airplane, but realize that if you buy a "cheap" airplane it will quickly become very, very expensive. As for fuel... Don't bother running at more than 65%, and go with even less if you can. The last few knots really cost you. For example, in the Mooney Ovation that I fly, I can plan on 170 knots at 12 gph. Above that, every two knots costs me another gallon per hour! (I've seen 176 at 15 gph and 180 at 17 gph the two times that I pushed it for a few minutes... And then slowed right back down!)
For budgeting purposes, split things into two categories: Fixed and variable. Fixed costs include things like hangar rent and insurance, and the base fee for the annual inspection. Variable costs are things like fuel and maintenance. There is no set "price per hour" because if you fly only one hour per year, even a C172 is going to cost you well over $5,000/hour. So, the more you fly, the cheaper each hour is. Better yet, budget for the fixed costs and then figure out your variable cost and see how much you can afford to fly.
Hope this helps, and good luck!
