Smart Agent-Best Solution

The best I've found so far for cost and funtionality is from SitePal.

Scroll down to view the package price (excluding customisable knowledge database)

http://vhost.oddcast.com/vhost_minisite/index.php?email=1&affId=15630

the technical spec & pricing for customisable knowledge database-

http://vhost.oddcast.com/vhost_minisite/index.php?email=0&go=products/ai.html&changeNav=1


Alltogether works out at around $5000 (£3000)

Quote from the site:

'Imagine an agent that represents your business on the web 24/7, is never tired, never needs to be re-trained, knows all the prices in the store, remembers each customer by name and is able to chat with thousands of people simultaneously, in any language.'