I have looked at many (but not all) business eCommerce "solutions" from open source to high-end, full-blown packages with all the bells and whistles - and in the end, it comes down to "you get what you pay for."
Open source is, to be sure, the most affordable route to take... IF you have no intentions of customizing your site to be just how you want it to be. Otherwise, you will have to be a programmer or pay a good chunk of money to someone else that can do the customization for you.
The commercial packages vary greatly in complexity, flexibility, usability, applicability, and affordability. I have seen some commercial eCommerce packages costing less than $100US that blow away rival packages costing thousands.
The key is to look around; do your homework. Check out as many packages as you can to find exactly what you are looking for. Some basic features to look for include:
Inviting and attractive design
Ease of administrative tasks
Smooth, trustworthy check-out process
One important thing to remember when dealing with an eCommerce solution is to back up early and often. This rings true with ANY computer-based activity. Read that again. Memorize it. Live by it.
Hope this has helped.