Create a simple admin where user can modify fields on a form

We have a form on our website where people can sign up for a charity event. There are different payment amounts that a visitor can select depending on how much money they wish to donate. Each checkbox has an amount and a label. Below the checkbox is some basic text. There is javascript that totals the amount(s) that were selected. When the user hits submit, an email is sent to admin with details of what was selected. We want a freelancer to create a login area whereby we can add/edit/delete the payment amounts and labels so that the form will update accordingly. Also there would be a textarea in the admin where we can put some free form text that also displays on the page. This should be done with PHP