ESRI Javascript API is FREE

http://gisprog.wordpress.com/2008/06/20/176/

ESRI Javascript API is FREE
The JavaScript API’s are not part of the ArcGIS Server installation, but are being made available (for FREE!) to any JavaScript developers out on the Web. You can start using them right now with your 9.3 RC1 ArcGIS Server.
They are available at:http://resources.esri.com/arcgisserver/index.cfm?fa=JSAPIsThe new resource centers have all of the downloads for the JavaScript API’s, Samples, SDK, and documentation.