Suggestions for cheap carseat for airplane travel

[fiona_var]

I am planning on buying a Radian to use in my car. My issue is regarding plane travel. I am waiting to adopt a baby/toddler. I think I will get my referral in October and will likely travel internationally to pick him/her up in December. I am not sure of the age of the child and know that it is possible to do a "lap seat" if the child is under 2. I would prefer not to do the "lap seat", if possible. Anyway, since the child will not be traveling with me to the first destination, the car seat will likely have to be checked. I am not sure which airline I will be traveling with, but if it is Air Canada they say that a car seat cannot be gate checked. I also know that the Radian will not fit carry-on requirements. I really don't want my Radian bouncing around with the other luggage, as I won't know if it is damaged and I hope to use it for many years.

I was wondering if people can give me suggestions for cheap car seats (safe for planes). If the baby is under 20 lbs., I can use my brother's infant car seat. I think there is a pretty good chance that the child will be more than 20 lbs. I don't know anyone else who has a car seat for an older child that is not being used. The other thing I wonder is if it is safe to buy a used car seat for this one trip. I wouldn't do this for the car but a plane is different than the car. I assume that the car seat's primary concern in a plane is to keep the child restrained in the event of turbulence. I have seen a few really cheap car seats in the USA but I know it is illegal to bring them into Canada (although they are compliant for air travel).

Thanks in advance for your suggestions.