Condition of the light bulb plays a large role in the value of these bulbs. Sputtering is a problem which causes the inside of the bulb to darken, and de-value the bulb. The Mickey bulb is very collectible and one that is lacking in my own collection (have a Donald Duck though). Prices have ranged anywhere from $100 up to $800 in years past. It's difficult to just stamp a value on something like this, so I don't - sorry. In mint condition, I might pay up to $150 for one, but no more. Others however may pay more. I guess it depends on the person who you're trying to market it to.
Is the bulb tubular in shape or round? I seem to recall the round versions are a little harder to come by. The spun metal base you mention isn't all that unusual and was a general (basic) model sold by Aerolux for many of their figural glow lamps. The Donald bulb I mentioned before also came with the same base, but in the copper finish with a hand painted image of Donald Duck. If your metal base has a similar painting of Mickey Mouse then I'd say it is very unique. Also for what it's worth, my Donald Bulb has an original sticker with Mickey Mouse shown on it and I've seen some Mickey bulbs with Donald Duck stickers.
Here's a photo of Donald for reference (note the labels mentioned above):
http://bulbcollector.com/gateway/Gas_Discharge_Lamps/Neon/Aerolux/Cartoon%20Characters/image/ne0038.jpg
