You mean like this?
Granted mine's a Jazz body but this is my Clement custom build. The pickups are both Duncans. The P is a Quarter Pounder and the MM is an SMB-4A.
They are run through a non-bypassable Bart preamp so the bass is active only.
This bass is a tone monster! But I will say that the assumption above that the MM will be louder than the P is not the case with this bass. When I have the pickup blend knob set flat, you definitely get more of the P pickup sound. I have to dial it back a little toward the MM to get a truly balanced sound.
I'm not somebody who worries about exact pickup placement. I get plenty of brightness from the MM and the Quarter Pounder is a beast up front.
Right now you can get both of those pickups for about $150 plus shipping. The place mine came from sells the MM for $85 and the Quarter Pounder P for $65. So thats your baseline cost. Where you go from there depends on whether you go active or passive. Its been said several times before that passive is definitely cheaper. Preamps can run $125 and up brand new plus it can be a little more work to do some of the wiring, though some sources prewire the pots for you so you only would have to wire the pickups, ground and jack.
For me, I've always liked active but I also have plenty of passive basses in my stable. Right now I have 4 passives, 2 full-on actives and one that does both and when I get bass #8 very soon it also does both. But I cant tell you which way is better for you. That's YOUR call.