well you gave reasons right there in your post why you would rather have macbook air than an iPad, so I don't understand what is your problem in making a decision? get the air and be done with it.
are there cheaper versions of ultraportable laptops? probably, but since you already got so much apple brand hardware you might as well keep going just for sake of compatibility issues.
Right on the first part - I'll stick with ruling the iPad out and get a laptop. the decision lies however, in what kind of laptop to purchase. I like the Air's design, as it aims towards what I'm looking for, but when you say its more compatible with what I have - not so much. I'm typing on a windows 7 desktop as we speak, and am looking for something to replace my windows 7 laptop, whether it be with another windows 7 laptop or not. (I'm replacing my current laptop because I want something lighter and less "portable desktop" type. it weighs 6 pounds or so). So I guess what I'm mainly asking now is, is there any portable laptops that are similar to the macbook air (thin, very light, easy to carry around and good battery life) ?