From WikiFarms
WikiService offers public and private wikis (German and English):
New developments become available to all wikis automatically and without charge. There is no upgrading policy. Prices are projected to fall about 5-15% per year (10% Dec 03). We aim at providing reliable and stable project frameworks for successful individual wiki projects, not at mass production.
There are FreeWikisForSchools. Wikis in public interest (or for non-profit organizations) may be given free or at reduced prices.
Is this cheap? or expensive? you can run an AspWiki on any ASP hosting service - for free.
This is cheap if you really want to start a wiki. You get a full-featured Wiki, free access to seeding pages, a maintained WikiEngine that is updated every few days, lots of extensions you can choose from, direct contact to the software development to discuss problem and future requirements, and help with all wiki related problems. For <10% of your total cost of ownership you can increase your success probability from 10% up to 95%.
Wikis are 30% technical and 70% social phenomena. While we try to provide the best possible wiki server, and push the limits wherever we can, and think that this is important - we know that social elements are equally important to the success of wikis. The necessary know-how is available from MeatballWiki (English) and GründerWiki (German) or by consulting us (free) and we are constantly working to increase our system knowledge and the general exchange of wiki and online community experiences.