How old is your lo, and about how tall, weight, etc? What car do your parents drive? Cosco Scenera is a good travel seat, but if your lo is bigger, it won't last long. Do you have one that you can fly with, assuming lo has a seat, I'd bring yours and use it on the airplane.
We bought the Cosco Scenera for both sets of grandparents because we were tired of having to transfer our car seat every time they wanted to pick her up. I did a lot of research and it had great ratings. I'm thinking it was $40-ish at Walmart/Target, since we had already bought two Graco MyRide65's for our cars, we were looking for something a little more economical to buy for them. The somehow managed to inherit both of my Graco's so when the new LO outgrows his infant car seat we will be in the market to buy ourselves new seats. Oh well, as long as they are both safe in whatever car they are in I'm fine.