Richard, you mentioned in previous posts that you work for an insurance company so I will assume it is a medium sized company, and my advice here is for a medium sized company, not the typical small startup business.
£45000 sounds a lot, but for large companies looking for enterprise or large scale content management systems, it is not the most expensive system, there are companies like Vignette selling their solutions to some companies for 6 or 7 figure sums! Are these systems worth it? Personally I doubt it, unless they give you what you need and are cheaper than making it yourself in a bespoke or semi-bespoke way.
At the other end of the financial scale you have the free open source systems, which I would certainly consider as park of a semi-bespoke project if I was in charge of a medium/large size company's IT strategy.
But a lot can be down to what your company's IT strategy is, regardless of what your business needs are. You might be open source all the way, on the other hand you might be Microsoft platform and tools all the way, so this might limit your choice from day 1.
Either way, analyse what your tie ins would be with any supplier. Would you get the source code or would there be an escrow agreement in place? Any company that is just focused on selling their own CMS will have a hard time over the next few years and might not be around for long, since they will face increasing competition from the open source crowd below and the main players in this market above. If their system is good enough and better priced than the main player's systems then they might be able to de-throne the main players and have a more secure future.