Do you mean traveling by plane? If you are traveling by car I'd take the Apex. A child is safest harnessed, so even if the seat feels "flimsy" it's better than a booster.
If you are flying you need to know a few things. First, you cannot use a booster on the plane. So, you will have to carry it on or pack it in your luggage. Some people carry the LBB, and pack the back in with clothes, et. Then, even if the luggage is lost they have something for the child to ride in. Then, you need to consier your DD's maturity. Has hse ever sat in a booster? Will she sit correctly the entire time- even when sleeping?
My DD is 4.5 and over 40 lbs and sometimes sits in a booster. I really like her Parkway because even if she falls asleep she stays in position. Most of the seats (Evenflo, Graco, etc) available at wa-mart type stores just don't have that sleep support- but it really depends on your child.
Do you have a few days? You could order a Parkway and get it in just a few days from several sites. It's on sale for a really reasonable price. Or, you could get another harnessed seat, but that would be over your $50.