Depends on if you are looking for pet or show and eggs can be difficult to hatch (but I haven't given up yet!)
Average I've seen between $50 - $125 each and usually the purchase of a pair is required.
Try googling - SCNA (Serama Council of North America) founded by the original importer of the Serama chicken; there is a breeder listing page. There is also an American Serama club that I think is focusing on breeding for standardized APA type but the group doesn't have a breeder listing page.
There are also two threads in the Breeds, Gentics and Showing forum - Amercian Serama and Traditional Serama, both are pretty active threads. I think there may also be an auction or two on this site.
ETA: price range above is for 6 month to 2 year old chickens
Yeah, I agree with Laingcroft.
Definitely check out the breed thread here on BYC and contact some of the breeders in your area.
Also, the auctions here are a very good resource.
Serama eggs (especially shipped Serama eggs) are more difficult than most to hatch, but I've had good success hatching them.
A lot has to do with the fertility of the eggs.