Numismedia lists it at $90, so, I wouldn't pay more than that personally. I don't go by NGC or PCGS price guides as they are normally way sky high on stuff, (tempting you to submit) I don't collect proof quarters so, I'm curious as to what the other members say. It does appear to be a top pop though, that's always nice.
Why would you think the grade is incorrect? NGC gets it right far more often than they don't. And, if you ever want to get a reasonable feel for a price, check out the Heritage archives. Looks like a reasonable price band is $50 - $90, depending on the strength of the cameo: http://coins.ha.com/c/search-result...71&Ntt=1963&ic4=Refine-CoinDesignation-102615
Assuming the OP is looking very specifically for a 1963 in 69CAM, NGC alone has graded 352 of them. I don't know what the OP's goals are in buying this coin, but high grade proof Washingtons, even those with cameos, are incredibly common.
Like you say, they're incredibly common. No major goal on this coin from where I sit. I kinda liked the older slab more then anything.