I just listed my Yamaha YBS90 keyboard bag on eBay.
http://cgi.ebay.com/Yamaha-YBS90-keyboard-bag-for-S90-or-Roland-FP-5_W0QQitemZ190017591135

Starting bid: $40

It is made for the Yamaha S90 keyboard. I used it for a Roland FP-5 digital piano which fit perfectly. Other 88-key keyboards may fit as well. Dimensions are below.

Features
- 1.5 in. foam padding
- Dual zipper pulls, lockable with consumer added padlock
- 14 in. padded shoulder strap
- "Hands free" towing capability
- 3 pleated accessory pockets
- Corner guards
- Inset wheels
- 4 runners protect the back

Dimensions
- Interior: 53 x 15 x 5.5 in.
- Exterior: 58 x 17 x 7.5 in