Bear in mind that he hasn't actually specified whether or not he wants a custom built or customized CMS and ecommerce system. If those were needing to be custom built, I can easily believe cam's price - and more.
If not, if you could use, say, Mambo and some basic PayPal ecommerce thing - it may be significantly less, but I still wouldn't charge less than $1K for something like that. (I'm just starting out, though).
Just tell them that big commercial CMSes can cost $10K-$100K.
Shit ain't cheap.