Simply click the financing option below that best meets your needs and fill out the form to qualify. Calculate exactly how much you can afford in terms of price and then figure out what monthly payments fit that budget.How should I write up an agreement to sell a vehicle at weekly payments? This document terms as the source for defining all the terms and conditions that are required while setting up a sale and purchase of a car. When financing through a dealer, always negotiate the car price first. Once the price is settled, then negotiate the monthly payment amount. A car sale payment agreement is used when the purchase price of the car is paid in instalments. A vehicle payment plan agreement is a contract between a buyer and seller of a vehicle that agrees to installment payments.