Certainly at a price tag of $250, I'd pick up an NGP. Will it come out at that price? I don't think so, in any form. Like a poster stated above, if Sony was going to sell anywhere near that price, they would have declared it already. As it is, I don't see the 3DS being effected at all by the NGP, nor vice versa. Outside of them both being handhelds, they offer completely different experiences imo.
If the NGP does launch at $250 though, it will be the first time that I will own and actively play two different handheld systems.