Maybe an nice double sided outdoor sign like this one:
http://milwaukee.craigslist.org/ele/2173973476.html
But not some cheap cardboard, wood framed, 60-watt lightbulb lit sign like the one he's selling.
FWIW, here's my question to him:
Hi,
You're way out in left field with the price on this RCA sign, but I still want it. Would you be willing to make a trade+cash? I have a vintage Coca Cola metal cooler to offer. I'm thinking the cooler+$50?
And his response:
Maybe I am out in left field? I don't know that for sure unless you can show me where someone else has one that is in the same condition for a much lower price. Please direct me to their item so I can see for myself. For the time being, I'm sticking to the price. I appreciate your offer but I am going to have to pass on it.
So in other words, it's just like kc8adu said- somewhere along the line, this guy saw some highly collectable sign go for $500 and thought they were all valuable. No harm in trying to sell this one for $350 he figures. Riiiight...