I've developed a hosted content management and ecommerce system to cater for most standard content management requirements. Prices start from £7.50 per month.

If you have specialist requirements, I can build additional modules for Omnium, or build a system from scratch.

Open Source (FREE) Content Management Software

Ecommerce software is available for free on the internet. If you chose to go down this route, particularly if you're hiring somebody to install it for you, please be aware of the following

• open source software is regularly updated
  minor updates can be ignored, but security updates will require attention. If you don't have the skills to apply the updates yourself, it can get expensive. Security updates usually need to be applied every two months.
• open source software requires higher quality hosting
  don't expect to host your content managed website on a £2.50 a month host. Most open source solutions need dedicated hosting if you're expecting anything more than minimal traffic. You can hire a self-managed a server at £50 a month, but if you're not clued up with servers, a managed solution comes in at around £200 a month 
• modifications also need updating
  add-ons are built by the open source community for the major ecommerce solutions, and made freely available. As security updates are applied to the core package, many of these add-ons break, requiring additional time trawling around the internet for fixes. If you don't have the time or skills to do this for yourself, it's going to get even more expensive.
• and if you don't update
  Hosting hacks are common, where visitors can install their own software (usually spyware) or text on your website.

A properly updated content managed site using open source software and getting a reasonable amount of traffic will cost around £300 per month, anybody charging you less is cutting corners.