There are a lot of cars you can buy for P50, 000. However, if you will continue looking in an area limited to only Olongapo, you will have a hard time looking for one.
If you will try to go down south to Metro Manila, there are a lot of Cheap Used Cars shop where you can find one. At Used Cars Express, located in Ortigas, Pasig City, you can find cars that are sold at a very low price. One time I saw a 1992 Toyota Corolla sold for P60, 000 and a 1986 Mitsubishi Lancer for only P50, 000. However, I saw those last year and I believe they have lowered the price of those cars even more, I just cannot guarantee that they are still selling those that I mentioned.
Also, if you are interested in buying an old SUV for your money, I am selling the old vehicle I acquired from my family a few years ago. I have not been using it for almost 2 years now but I guarantee that it still is working fine. It is a white 1982 Toyota Liteace. I think its better off selling it than just putting it my backyard.
If you want you can contact me at +639263786494 and look for Alvin.