Are you kidding? They wouldn't let you take a helmet as carry-on?!?!?
Just recently, I had accidently left a 5mm allen wrench in my messenger bag and the TSA creep found it. She just kept saying "TOOLS ARE NOT AUTHORIZED!" over and over again and called the supervisor and the local cops over like I was a war criminal or something... I don't even think Boeing builds planes with metric hardware

So, they confiscated one of my most used tools, but completely missed the pair of scissors that I had also accidently left in there.
BTW, helmets are not on the list of prohibited items from the TSA, so I'd probably print out the list and make an issue out of it if I had the time. I'd point out that it may be required by law where you're going and bring up the AMA, NHTSA, whoever...
http://www.tsa.gov/interweb/assetlibrary/Permitted_Prohibited_7_24_2003.pdf
I wouldn't trust my helmet with baggage handlers, but if you do actually check the helmet as checked luggage, most companies just ship them in double cardboard boxes. I'd do that, maybe some extra bubble wrap, a bright orange fragile sticker and hope for the best.
As for the original question, I've seen and tried on some KBC helmets and was pretty suprised by the apparent quality and comfort. Even the best KBC can be had for just over $200 and they meet every safety standard you can think of.
The AGV Demon is another excellent helmet that is available for under $200. DOT/Snell and pretty cush, too. If you do look at the AGVs, I'd recommend trying one on first. AGV sizing seems to be different than other brands, and I actually received one from mail-order that had a size sticker on it that didn't actually match what the individual parts said they were.
BTW, most of the big mail-order helmet shops have a huge re-stocking fee for returns (like 10% or $25), so if you go that way, be sure that you're getting the right thing.
--Fillmore
(Can you tell that lots of travel has made me bitter about this whole TSA thing? The more that I deal with them, the less that I believe that they do anything to improve safety)