Greetings from the Florida Panhandle
First off, Welcome to the Forums. We're glad to have you with us.
As to your questions, the Excella model name was one used by Airstream a number of years ago. I can not think of any reason why Excellas should be any less expensive than other models. Older Airstreams' values are usually directly related to the condition of the unit in question.
Generally speaking, amongst late model Airstreams, the larger the unit, the greater the price. Vintage Airstreams are just the opposite, the smaller the unit, the greater to price.
Tell us more about your wishes and situation. We might be able to make better suggestions. Don't overlook the fact that when you get into the larger late model Airstreams, a substantial tow vehicle will be needed.
Be sure to check out the Classifieds section here on Airforums.
SuEllyn & Brian McCabe
WBCCI #3628 -- AIR #14872 -- TAC #FL-7
2015 FC 25' FB (Lucy) with HAHA
2005 Suburban 2500 Quadrasteer (Olivia) & 2011 Silverado 3500 (Fred) with Outfitter Truck Camper (Ethel)