The only aftermarket part you NEED on a P07 is the firing pin retaining pin, which is under $10.
P07+a few parts+ basic milling= about the same price as an MOS Glock. Really a wash once you add holsters and the dot.... Maybe a 10% price difference?
One new option you might consider is the upcoming Grand Power MK23, which are going to be optics ready from the factory.