I use 48s for the boys, and 42s for the girls when I use crates at all. Right now I have a boy in a 4'x4' x-pen with a lid, that has three sides so that he can go through the doggy door to a kennel outside.
They, all of them, can fit in a 36" travel carrier, rather comfortably. They are more square than a crate though, and the dogs just fold themselves up and go to sleep.
I never considered a crate or x-pen from e-bay. Will definitely check them out the next time I am looking for something.
Jenna, RN CGC & Babs, CD RA CGC HIC
Heidi, RA CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear CGC