First of all I'm not arguing in favour of either the P-1 or the P-8, but I would offer the following word of caution. Don't get too focused on the purchase costs of an airframe. The long term support costs for an aircraft far outweigh the initial purchase price.
So we have aircraft A and aircraft B to chose from, both with acceptable performance levels. Aircraft A is cheaper to buy, but more expensive to run, than aircraft B. So while A might appear the better option, B is actually the more cost effective in the long term.
Of course if your budget is limited in the purchase phase then that may sway the argument........but you end up paying in the long term.
I should also point out that I haven't a clue what the purchase price of a P-1 or P-8 is, or their relative long term support costs!!