Have you considered an open-source N2 CMS (http://n2cms.com/)? That one is pretty impressive! It's developed on .NET (using NHibernate as DAL), the code is clean and the engine is very developing-friendly - it has an API to support third-party plug-ins and actually may be a module itself for an existing web-site. I mean you can use N2 as a plug-in to your e-commerce web-site. It lives in its own folder and a couple of tables in the database, it even may use it's own LiteSQL file.
I'm pretty sure you'll save tons of time if you reuse the existing one rather than developing yours from scratch.
By the way I have a question - what's your business model? How are you going to earn money? Will I have a risk to be charged ~$1K after the first year? ;)