We used a playpen for Soph for the same reason. Dog kennels and X-pens were sooooo expensive. Plus, the bottom of the playpen is removable and VINYL so it protects the floor and is easier to clean up when the "baby" misses the potty pads. Also great if you've got one that likes to play with the potty pads while you're gone and wad them up
. With the vinyl bottom your floor is still protected. They're portable, fold up easily, and mine has wheels so it's easy to move around the house.