If I were to guess, by the sale prices of similar AM facilities in St. Louis, WGNU would probably fetch somewhere in the neighborhood of $1 - $1.5 Million. As for WSDZ, I doubt Disney will be selling it soon, but with the improvements to the signal that they have made - Their 20kW daytime signal is one of the best in the market. It would be a lot tougher to put a value on it, but I would guesstimate in the $3 Million neighborhood.
I'm judging my guesses by recent sale prices of KSLG, WESL, and WDID over the last 18 months or so. Anyone buying either of these properties would be doing so only for the signal. WSDZ is Radio Disney, and WGNU has really went to pot since the death of its founder Chuck Norman a couple of years ago. WGNU, while not billing well these days, does have a heratige as an eclectic talk station for many years, that probably could resume under new ownership.