Keep in mind that the way they do the stock pix in the Showcase doesn't always make the flame show up as well as it could. I've never ordered a flame/birdseye neck custom, but I would suspect if you look the differentiation of the std. priced vs. the premium priced necks on the showcase it would give you some guideline to go by, typically the flaming will not be as pronounced or be as uniform through the neck.
I think most of the really premium pieces of flame/birdseye wind up in the Showcase at uber premium pricing which they WILL command.
Also, be sure to check the web "specials" and the category of neck wood you're looking for every day. I've picked up a couple of AAA/AAA+ necks from Warmoth really cheap (one was $125 the other "as maple" for $157) do to some very minor flaws - one had a tiny sanding burn on the underside of the peghead and the guy that burns the "Warmoth Radius" came back from lunch stoned on the other one cause the brand was a little off and you could just see the edge of the "s" peeping past the neck pocket.
Additionally, you can sometimes find deals on what I guess are returns, as they are already fretted/nutted. You have to check constantly as any kind of deal on the website doesn't last very long....