To me, the warranty of buying a new gun has some worth, apart from the lack of wear on a used gun. So, buying even a LNIB, unfired without warranty Nano, would have to be discounted for me. Only the individual buyer, however, can judge the value of a product to him/her.
For a new gun, Buds has them at $378 shipped, Grabagun at $377 shipped, Kentuckygunco at $376 shipped. My rule of thumb on used gun buying is that a used gun in excellent condition should be around 20% less than the same new gun. Right now, I can get a new Nano shipped to me for $401 (including my $25 transfer fee). I would want to pay not much more than $320 for a used Nano.
Checking gunbroker and looking at completed auctions we see a range in selling prices. Many have sold for between $275 - $300, although that does not include shipping and transfer fee, if necessary. I would certainly not want to pay more for a pistol than I would pay for one at an auction, unless there was some other value added (e.g. you can carefully inspect the gun, or test fire it).
So, I would not consider anything over $350 a good deal, even for a motivated buyer. I would say that anything under $300 is a good deal, while $300-350 should be an average market price.