I want a writer to write a short and simple Payment Agreement Contract for me. t

I've started my own company and I am looking for someone who is familiar with law to write a Payment Agreement Contact for me. I would like to be able to plug in the price and have a soace for the customer to sign and date at the bottom. I would like for the contract to say that the customer is giving me permission to work while promissing to pay me after i have completed my work.