I would say that, weight aside, the limiting factor for most o/o when it comes to big bunks is the price. Many companies don't pay their o/o well- FAF is one that has been mentioned in this thread. Their rates are very low for o/o. And to support a truck payment is hard enough- add the price of a custom sleeper and you might just be asking for problems.

Even used big bunks (if you can find one that's not already off the market) are pretty pricey.

ARI, ICT and Double Eagle are very, very proud of their products. The average ARI sleeper costs more than my house did. Granted, it's a small house in the middle of nowhere...