Apparently they produced tons of prints. From answers.com:
"Ullman Mfg. Co. mass produced lots and lots of prints and photographs, and distributed them widely. Some prints may be easier to find than others, however.
Bear in mind the value of an item is dictated by how readily available it is in the marketplace at the time a person decides to buy, how much the buyer wants the print, and competition from other buyers. If someone documents the available prints and other ephemera, collectors may show more interest, leading to an increase in value.
In general, Ullman framed lithographs sell for $35-90 in online auctions and on commercial websites, and sometimes for a little more, $115-140, at live auctions. Antique stores tend to overprice the merchandise: recent [December 2010] prices recorded from common prints with price tags of $195 (Swinburne Seascape) to $375 (Priscilla, "Why don't you speak for yourself, John?"). To put this in perspective, the identical framed Priscilla image sold at auction for $80 in 2006, and for $25 in 2008.
Ullman postcards are also plentiful and cheap, ranging in price from $2-20, with most selling in the $4-10 range. Due to the wide variety they're inexpensive and fun to collect, but they have virtually no investment value at this time."