A crinoline is a must-have for any rockabilly kitten and here are some etsy shops that I frequent often that carry them at a decent price.
Prices run from $20-50 mostly and this shop carries a good steady stream of adorable stuff, including pettipants! When I want a crinoline, I check here first. This cute turquoise crinoline is a mere $28.
This shop has a couple of crinolines right now of different styles, including this black and pink trim gem from the 50s for $39. Hurry, because I have my eye on this one...
One last point on crinolines- don't be afraid to get a square-dance crinoline and cut a layer out to make it lay better with a rockabilly skirt or dress. If you are careful, you can actually use the bit you've cut away to make another crinoline by attaching it to a new yoke (which is basically a rectangle of similar fabric turned over at the top for a piece of elastic). Take the time to inspect the crinoline before you cut- I ruined one by just hacking into it and realizing that it wasn't constructed the way I thought.