I used to collect antique still banks. Yours is listed in in Moore's "The Penny Bank Book". It lists it as an Elf, and the design was originally cast as a door stop, but the factory later changed the mold to include the coin slot so as to produce it as a bank. It is known as a 'factory conversion'. The book lists it's scarcity rating as 'C' which is "getting hard to find". It does not date it, but I would imagine it is late 1930's. very cool find. too bad it wasn't full of coins.
that's a tough question.... typically cast iron banks in nice condition with original paint sell in a common range from say 35 bucks to 100 bucks or so on feebay, depending on subject and rarity. yours is in somewhat rough condition, so of course that detracts from value. blasting and repainting would stop the rust, but detract from value as well because it takes away from being original. Personally, I would say maybe 20 bucks at best. If it were mine, I would probably try to get it sand blasted, and repaint it in original colors and just enjoy it for what it is.