Please explain preamps for me

[Intamin]

Title says it all. I don't understand why preamps, or processors, are all more expensive than an avr that includes the amps? It would seem to me that the avr should be more expensive than the preamp, since more is included. Also, have people had much luck using avr's as pres to separate amps? Finally, any brands out there that make a pre in the sub $2000 range, the only thing I can think of is the Integra 9.8. I'm just trying to figure out the best combo for the money. Currently it's looking like an Integra 7.8 with an anthem statement a2 amp that checks in at 2500 msrp. Thoughts on combos and an explanation as to why pres cost more would be great!