As ducklite posted, none of the DVC resorts have rollaways or cots available. Since BCV is also a DVC resort, I'm sure that will be the case there as well.
I'm not an expert on Expedia, but I did just check availability of BCV rooms there for the fun of it. (FWIW, IMHO, $189 plus tax for a studio is a very good rate). If you select "Book it", this info comes up on the Rate Detail screen:
"Other options
You may request the following items from this lodging.
!Availability of these options is not guaranteed by Travelscape, Inc. or Expedia, Inc.
Adult roll-away bed: $0.00 No charge
Child roll-away bed: $0.00 No charge
Crib: $0.00 No charge"
I believe EXPEDIA has the wrong info, especially since this is what comes up for the Beach Club Hotel rooms:
"Other options
You may request the following items from this lodging.
Availability of these options is not guaranteed by Travelscape, Inc. or Expedia, Inc.
Adult roll-away bed: Not offered
Child roll-away bed: Not offered
Crib: $0.00 No charge"
Don't count on getting an extra bed from any of the DVC resorts. Some people do bring an air mattress if they have children who do not want to share a bed. This can make for cramped quarters though.
Enjoy your trip