Implement a document management system (hosted)

As a manufacturer, I am getting lots of documents (plans, contracts, etc.) from suppliers and they are all with different file types, names, etc. I need a document management system that has features to ensure: Only the latest plans are available at any time; old documents are stored in archive; people who are listed should be informed by email or SMS if a new document arrives, etc. It needs to be very easy to use, as many people in the company are not IT literate. Cost is very important factor - so the cheaper the better, as long as it delivers high security.