Charlie- You didn't mention what cheap is to you but in my experience AV preamp are generally higher end products and would be more expensive. I even had a heck of a time finding an AV integrated. NAD makes them at fairly low price point (think I paid about $350 new for a prologic unit). A sub will really improve your enjoyment of movies and you'll need rears for surround. A prologic unit would be pretty cheap now, but DD is definately worth the extra $. You will definately want a center channel speaker.
AV PreAmp vs. AV Receiver
I would like to be able to easily switch from VCR to DVD to DVD/CD use in an inexpensive 2 channel system by/for the TV. I have a cheap (in place) Onkyo two channel receiver and another integrated amp that can be considered for use. None are "AV" designed. Would I do best to get a cheap new "AV" receiver, or would the addition of an "AV" preamp give me the best performance, (within the same price range?) This is not for critical listening, just for TV/movie sound and background music. Will be pumped through some PSB 300i speakers. May add a sub later. Thanks for your help. Charlie