cd multi players - new corolla owner

I'm about to take delivery of my new Toyota Corolla (1.6 GS Auto), and I want a CD multi-player.

The price as an extra from the dealer is clearly outrageous.

I've determined that a Sony CDX-646 can be fitted, and controlled from the standard head unit (this is what one auto hi-fi place said anyway).

Anyway can anyone tell me if its just the Sony CDX-646 that I will need ? (can I go out and shop for the cheapest one I can get ?) Or do I need some convertor and lead to run to the head unit ?

Will any other Cd players work with minimal work ? Where is the best place to fit the thing, in the boot ?, where ?

Is there a cheaper source than the dealers for the Toyota original kit ?

Cheers etc!

Value my car