look on craigslist under "roadie case". You'll find one that can work suitably well, you might just have to play bidding games with people.
depending on your location as well, the closer you are to a major metropolis(like LA or NY), you'll have better luck, but you never know.
be patient. Also look at re-doing the interior, when I bought my road case it was designed for a telescope, but it fit approx 40 holders nicely with the new padding and dividers inside.
-Dan