Create a custom excel plugin

We need to create an excel function (plugin) that will call data from a MySQL database that we will maintain seperately. the format should be as follows: =ourfunction(input) where: OURFUNCTION is the excel function we need to create INPUT is the key for the data we want to look up from the MySQL datatable The function should return the value that gets looked up in the from the table. The database will need to allow gfor multiple users and be password protected so there should be a way to enter the username and password into the excel plugin, either a dialog box or a menu item. Ideally please be familiar with ubuntu linux, our preferred database platform from a cost standpoint. We will need help setting up the database initially with digital ocean, our cloud provider. We are very cost conscious so are open to the idea of using a third party toolkit.