I recently read a great HBS case study on Rent the Runway, and we've recently completed a tuxedo rental e-commerce site for another competitor of the Black Tux.

The economics of it might look something like this:

Middle-Tier Tux:
Retail price of tuxedo $500
Wholesale cost of tuxedo $215
Cost of tuxedo to online retailer $150 (negotiated)
Revenue per rental $60 (just the tuxedo, not accessories)
Variable cost per rental $20 (shipping, stains, cleaning, etc.)

So if you're paying $150 for the tuxedo, and you rent it out just 4 times, you'll be above break even ($60/rental - $20/rental/fixes = $40 profit / rental, x 4 = $160).

This is a real world example FYI. In terms of inventory requirements, that's going to depend upon your business. Rent the Runway has TONS of dresses. But they started out with a limited supply and grew from there. The Black Tux keeps their selection limited and high quality, which I'm sure helps them manage their inventory easily, run numbers constantly and make sure they are running everything appropriately from an inventory standpoint. I wouldn't be surprised if they had product ready to be added to their distribution at the drop of a hat, especially for busier seasons such as prom or summer (weddings).

I hope that helps. Happy to answer more questions for you.