Cuda, I have found there is so much work that needs to be done in building a business and an ecommerce website, that even though I have a degree in computer science I still find myself wanting someone else to do the technical work while I concentrate on the business aspect.
No matter the web technology used, the business aspect requires pictures, sales information, prices and product permutations, product warranty, return policy, and more. The content of the site is so exhausting to develop, it is own project. Being the person responsible for the business content, site development, order taking and shipping, financial accounting, inventory management, and product development is an extremely daunting task.
Shopify has transaction fees of 2% to 1%.
Yahoo small business has transaction fees of 1.5%-.75%. Yahoo's prices have come down in the past year. They used to be 3%-4%.
Magento does not have transaction fees.
IMO, transaction fees are inappropriate since website construction and use is not related to purchase transactions and amounts. I would rather pay a flat fee per month than a transaction fee. But as I mentioned earlier, maybe it is better just to get into the game with any of them to get sales started. A running operation can be modified later when cash is flowing much easier than taking the difficult route to build a website that may cost more over the long run in lost sales just to avoid transaction fees.
EDIT:
Volusion is another website builder and shopping cart provider with
no transaction fees. I believe they rely on Microsoft's ASP.