For drop-in simplicity, I'd go with these Audiobahn plate components for $100. Very efficient with external, switchable crossovers.
Audiobahn 6x8 Plate Components [img]
http://store6.yimg.com/I/competitiondirect_1657_57261245[/img]
The Crystal 5x7s from
www.mmxpress.com are supposed to be excellent speakers with external crossovers. Unfortunately, they're now $175 for two pairs (used to be $145).
Crystal 5x7s with external crossovers 
The cheapest drop-ins of the 5x7/6x8 variety that I can find are these other Audiobahn plate components at $46. I just wouldn't use them without a sub, and I'd make sure to use a hi-pass crossover with them. No external crossovers, tho.
Audiobahn Plates [img]
http://store6.yimg.com/I/competitiondirect_1657_57889114[/img]
IMO, Rockford Fosgate and Cerwin Vega both seem a bit overpriced for what you get, especially when you go to BB/CC for the 200% markup. With a little bit of work/research you can put together a set of custom components that will shame them for ~$75.
