Lots of people turn to cars under $1000 bucks looking save a buck or two. Here is a quick guide on how to make some cash (that you can use to buy more rusty boxes on wheels of course)
Plain and simple part cars out.
Step 1. Buy a car. This is pretty much the most crucial step. If you are actually doing this to make money and not just salvaging that blown up buick sitting in your driveway than you need to find a car that people want to buy parts for. eBay is pretty much your friend here and my suggested avenue for selling most parts. In the past I have watched people make money from a variety of cars (my roommate used to finance his workshop with parted out cars) One in particular was a 1994 Honda Accord. Thats right you don't need to buy a 1939 Alfa Romeo (although that would be sweet) or anything super rare to get good money for parts.
Often times finding a car that is pretty common can be a good thing but be sure to check eBay for the prices certain parts are going for before hand and let that be your guide in making your purchase. Now when it comes to buying the car usually the ones that don't run will be your best deals and you may even get a freebie if your lucky. (few people want dead cars in their driveway) Obviously the less you pay the more you profit.
Step 2. Tear it apart. The key here is research and time management. Everybody wants to pull the engine and trans etc., but often times it may not even be worth it. Check out eBay or where ever you plan on selling and ask yourself is what these parts are selling for worth my time? Would I actually want to crate and ship this? Is anybody actually bidding on this crap? All good questions that need answers. Honestly it tends to be the nickel and dime parts that can really make you some money. Shifters, speedometers, sensors, mirrors, sun-visors, etc. these parts take seconds to remove and if they are in good shape people are often willing to pay a pretty penny for them, because the only other option for parts like these tends to be the dealers who charge an arm and a leg.
Step 3. Sell The Parts. Once you have determined what you want to sell and pulled the stuff off its time to start selling. I like eBay but swap meets, forums, and other sources may work better for you. If you have done your research you know where to find the people who see value in the parts you have pulled.
Step 4. Scrap the rest. Always factor in that you can prolly get $100-$300 bucks for the rest of the pile at the scrap yard. Usually you will want to haul it there yourself and will probably need to pull the tires and gas tank. I would even consider it a good rule of thumb to try and not pay more for the car than you can scrap it for. This helps you avoid any kind of loss.
And there you have it. Four easy steps to make some quick money and make your neighbors hate you.