I have an 1964 Airline round set in a black enameled metal cabinet which is probably a bottom of the line model...I agree with Andy, it looks a lot better than some of the monstrous wood cabinets!
Looking at a Sears catalog from 1965 (My Wards catalog from 1964 for some reason did not include color sets, they were in a separate brochure)
The cheapest 21" round set is $329.95 and the most expensive is $539.95.
The only things the most expensive set seems to have over the cheapest is a cabinet with legs, an extra speaker on the left side and automatic degaussing.
All of these sets as far as I know used the exact same chassis (which is a CTC-15 clone). I guess they sold the "sizzle" rather than the "steak"...as the cheapest set's performance would be almost identical with the most expensive.
Here are some scans of the round sets in the 1965 Sears catalog.
http://nipper.freeshell.org/pictures...nd_round-2.jpg
http://nipper.freeshell.org/pictures...sets_small.jpg