Your best bet would be if you would start putting that $300 a month into savings or some other sort of safe investment. You would save that $3600 per year and in a couple years down the road when it is time to buy, you will have a sizeable down payment (or be able to pay in full!) Then when you are done with payments, you can keep putting that $300 away each month. Then you have money set aside for repairs, or a down payment on your next vehicle if you decide not to repair.
Leasing a car is a sure fire way to lose money. The dealer knows that they will make money off the lease, the mandatory service at the dealership, and then the subsequent sale of the off-lease vehicle. You pay a sizeable down payment and then monthly payments as well as mandated service at dealer pricing and at the end you have nothing to show for it.