The Allan character is turning out to be a fan fave since the movie's release -- probably because he turns out to be an unsung hero in the plot -- and as you can imagine, folks have been wondering if Mattel has plans to re-release the toy.

For those unaware, the Allan doll was first rolled out in '64 as a friend of Ken's, but was discontinued a couple years later. Despite his newfound Hollywood relevance, Mattel recently announced its keeping Allan off store shelves. Bad news for all you Allan stans.

However, that news has impacted Allan's value in the open marketplace. TMZ did some digging, and there's been a major price surge over these past few days. On Thursday, we saw several eBay listings for old Allan dolls going for cheap ... about $35 to $76 a pop.

Come Monday, however ... a lot of those prices have multiplied. The vast majority of Allan's eBay listings are now at least $150, if not a lot more. There are some going for $300 and up.

It's basic economics -- the flick was hugely popular this weekend, and now that we know Mattel ain't putting any new Allans out into the world ... the demand is at a peak right now.

While the re-sale market won't really help Mattel's bottom line -- there are a lot of private sellers who stand to ride the "Barbie" movie's coattails and clean up as well.