A google Gadget Required.

We are starting a google site and it is still in the early days. While working on it we realized the need to have a gadget that could update a published google spreadsheet from the website itself. We do not want users to sign in using their google account for updating this. All we need at present is a box where a user enters a numeric value... and that value appears in my spreadsheet at a predefined cell. We do not want to use google forms because we have some other limitations. Please let me know about the feasibility and the charges for getting this job done. Amitesh.