I have to tell you that the really cheap strollers that are cabin-approved are actually really bad quality, rattly and getting loose. So my advice to keep it reasonably budget-friendly but not go crazy cheap, rather around average, especially if you really plan to use the stroller. Which is why I will suggest looking at Cybexes - their compact strollers are spacious enough so that your baby won't be craped or her head over the backrest already, and are rather small so very airplane friendly. From the Cybex Eezy2 to Cybex Beezy or even the simple Cybex Orfeo, I think you could be reasonably happy with the buy.
I don't know if you can get your hands on a Kinderkraft stroller but the Kinderkraft Indy (2) is also a rather ok choice.
The GB Pockit+ All-City or the GB Qbit, even if pre-owned, could also do you a nice service.