I have been through many different experiences, 2 years ago I started building my first online store on Yahoo stores. Found that their application was difficult to modify and was not very flexible for a beginner.
I then went to Volusion and found their application to be much better than what Yahoo offered. I stayed with them for about a year, but the amount of money I was paying out, made it unfeasible to continue paying almost $90+/month.
Then came the open-source... I figured why not try oscommerce. After many hours of continuous adding of modules, I found CRE Loaded which had an almost turn key version of oscommerce.
CRE Loaded is a pretty good piece, for someone selling normal material products. Doesn't require much knowledge of .php, easy to install, and has a wide variety of add-on templates available through a number of different online stores.
Unfortunately, CRE Loaded doesn't have a solid offline credit card processing module (kind of buggy) and their customer support is way behind the norm and somewhat unacceptable.
I found
CS-Cart Ecommerce Solution as the best solution so far. Although to software requires a license purchase for about $195, it is a one time fee and doesn't come back. Customer support has been wonderful and timely. CS-Cart offers many flexibilities, and is loaded with ecommerce features to include downloadable product capabilities.
I hope the above sheds some light to your concerns. My budget has been somewhat tight and dependant on sales I make. I would strongly recommend
CS-Cart.