I have no experience with MIM P basses. I've had several Fender MIA P basses, though.
And I have 1 MIA Fury.
I would spend $200 on a Fury over $400 or more on a MIM P bass any day of the week. Actually, I'd take the Fury even if the Fender was the same price. Heck, if the Fury was $200 and the MIM Fender was $100, I'd probably buy them both and then sell the Fender for enough to pay for them both.
My Fury already had a Hi-A (vintage Bartolini) pickup in it when I got it, but I would at least give the stock pickup some play time before I spent money on a replacement. The good thing is, you should be able to buy a nice Fury, a nice replacement pickup, and pay to have the pickup installed and the bass setup, all for less than the price of a good condition MIM Fender P.