A wordpress blog setup on its own domain and then tweaked is about as much website as most small businesses need – download a theme and install and you are done. Should take someone who knows what they are doing less than a day plus a bit for a logo and custom colour.
So that was easy… but when you chuck ecommerce into the mix it all gets tricky fairly quickly.
You can get free ecommerce plugins for WP (ie http://www.instinct.co.nz/e-commerce/) and if you are happy to integrate with paypal or google checkout then no big drama.
Otherwise:
Free, Medium weight: OS Commerce (good enough, templated looks a bit rubbish)
Free, Heavy weight; Drupal with Ubercart (very good and flexible but a major learning curve!)
Actinic looks tempting and could get you going quickly but it's a bit shit in the long run.
You may get better value out of a shopping cart system offered by an ISP (as above)
BUT as above – you need to sort out what you really want your site to be doing first (for instance are you going to extensively blog and sell off the side of that or just sell and do no blogging?).
Once you know what you are going to be doing then match the feature against the above systems (for instance do you need live stock levels? Do you need to integrate with a particular payment gateway other than paypal or google checkout) Do you want the system to automagically generate receipt emails etc etc etc. Mostly you don't need much to start with but realise that you will be doing a fair amount of running around after your site – all the money on expensive big sites goes into automating and streamlining.
You should probably spend just as much time on your email marketing (use Mail Chimp) and get your head around Google adwords as soon as your site is live!
That started as a few lines of advice 🙂
Good luck
A