If you are on a budget and concerned about price versus performance, I would recommend not buying a new model, but instead buying a refurbished model via a company like Other World Computing, Mac of All Trades or even directly from Apple.
In my experience, refurbished machines are as good as new and cost less. And in the case of Apple, they have the same 1 year warranty without having to pay anything else. And in many cases, the machines themselves are physically and operationally as good as new. Lots of times they are just returns from people who purchased the wrong machine or just decided to go with something else.
As far as MacBook Pro versus MacBook Air, the question of “power” is arbitrary at best. I do coding, systems administration and light graphic design work and I am using a Mac Mini. When I have used MacBook Air’s for this same level of work they work 100% fine for my needs. Some people feel they need “Pro” models because they have some self-exagerated requirements for the work they do; meaning they just want “the best” but honestly barely use the bells/whistles.
Unless you are doing some highly system intensive work—such as editing 8” x 11” photos at 1200dpi for pre-press or HD video work—then a MacBook Air is perfectly fine machine.