text chnage event in asp .net datagrid

[Manish]

Hello Everyone
I am trying to design a datagrid in asp .net, which pulls cateogry and
amount for each category based on criteria selected by user. Category
and amount are being populated from database in datagrid. There are
some categories like "Revenue" and "Cost", which are inter related in
a way that cost is always fixed %age of Revenue. For e.g.. Cost is 20%
of Revenue.
I want to reflect change in Cost as 20 % of Revenue, as soon as user
updates Revenue number. Also want to avoid making round trip to server
and want to do this on client side. Can someone guide me as to how to
achieve this? Do i need to use some java/vb script? Some sample code
will be really appreciated.

Thanks,
Manish