I recently got a fretless and had to find a good double electric bass gig bag. I searched all of the regular internet retailers. When I looked on Ebay I found a really nice one made by Pro Stage Gear (PSG), at a great price, and available at X Case Wholesale.
PSG's gig bags are built really well. They have separate zippered compartments for each bass. They also has nice 1" thick foam padding on each side and between the basses. There is even padding around the entire perimeter of each bass to protect the edges of the bass as well.
The cost is only $50 plus shipping. If you need a gig bag for one or two basses (they make both), you should check these out. They also have great prices on flight cases as well. They even have a cool gig bag/flight case combo that would be great if your touring.
Go to:
http://stores.ebay.com/XCase-Wholesale
In addition to a great product at a great price, they also have top notch customer service. My gig bag showed up with a tear on the inside and missing it's strap; I made Tim at X Case Wholesale aware of the problem and he immediately had Pro Stage Gear send out a replacement that was perfect.