Even though the NGP is supposedly easier to develop for than the 3DS (at least for ports and no stereo 3D), it also is capable of bigger budget titles (higher end graphics) than the 3DS.
Given that, I suspect the NGP's retail games will be between $34.99 and $44.99 to be competitively priced with 3DS games. Though, they may try a $39.99 to $49.99 price range if 3DS games move to that price first (which I wouldn't count out just yet...).
Also, on the topic of DD vs Physical games. I think physical will always be cheaper than DD, because the DD vendor has no competition (per platform) where as retail has tons of it. Add in the fact that DD has 0 resale value...you can clearly see where many shoppers will go. And, if you do away with the physical games market all together, the DD prices will go even higher since there would be no substitute or competing vendor.
