What green car could a kid in the US get for around 10-15grand?
I dont care about power (well I do for sports cars but this is not a sports car 
) I am interested in buying a green car. It can be gas powered, if it is a hybrid, or really fuel efficient. Again just recommend something. I dont have much money so anything below 15k would be cool. And insurance is expensive so please nothing to sporty.
a late 90′s or early 2000 diesel car
none. sry but thats the truth.
they sell vegetable oil mods on ebay so ur car can run on vegetable oil. costs about 1-2 grand
You could buy a 4 year-old used Prius or Civic hybrid… but be aware that the battery life on those vehicles is only about 8 years, so it is an expensive repair coming in a couple of years (around $2k).
Any diesel engine is more fuel efficient, and if you use low-sulphur diesel or bio diesel (not mandated in all states), you would have a "greener" vehicle.
A used Corolla, Camry, Civic, or a new subcompact would also get better mileage and burn less fuel. In fact, your driving style also really impacts fuel efficiency. The problem on these small vehicles is that people tend to try to accelerate too quickly, since they tend to have smaller engines.
A high mileage car is going to be "greener" than one with lower mileage. Here is a list of high mileage used vehicles: http://www.auto-broker-magic.com/gas-mileage.html A hybrid is known for higher city miles than highway miles. A used diesel is going to be a better value than a petrol vehicle due to the longer expected trouble free life of a diesel. The car which is frequently mentioned as better than a hybrid is the Jetta tdi. Some owners report mileage from 50 to 70 mpg on the highway. To get that kind of mileage you should become familiar with hypermiling techniques: http://www.hypermiling.com/car-mpg.html
Once you have a diesel vehicle that can achieve a high mileage and are familiar with the techniques of hypermiling to make it even more "green" you can switch to using biodiesel to further reduce your pollution footprint.
If you wanted to have a perfectly zero emissions vehicle you would have to have an electric vehicle. At this point you are willing to make more severe compromises on performance and mileage and might be willing to make many new friends as you stop by asking if you can charge your vehicle. Of these you would have to be looking for something that could achieve highway speeds but also had a long range. This puts most NEV (neighborhood electric vehicles) out of consideration.
A three wheeled vehicle is typically registered as a motorcycle and are generally cheaper as they avoid some of the safety standards required by automobiles. You can find some of these listed new here: http://www.evfinder.com/threewhlrs.htm
and used here:
http://www.austinev.org/evtradinpost/index.php?method=showhtmllist&list=classifiedscategory&fromfromlist=classifiedscategory&fromfrommethod=showhtmllist&fromfromid=13&clearoff=1
http://www.eaaev.org/eaaevsforsale.html
A lot depends on how much driving you intend to do. Try just getting a small car like a Dodge Caliber or Ford Focus. Their small size will give you fuel savings as long as you don’t drive them too hard.
You can get a really decent natural gas (methane) car for less than half that amount! My family has 3 of them and none were over $5800 used. Mine is a 1998 Ford Crown Victoria with just 57,000 miles on it and I got it last year for just $3000. Natural gas is super cheap where I live, but you’ll have to check if you have a place to fill up in your area. They are much greener than gasoline cars, plus natural gas is a lot easier on the engines so they last forever. You could probably get a nearly new Honda Civic GX for $15,000 if you’re wanting something almost new. Check eBay or Craigslist for cng cars and see what you come up with. Good luck!
I recommend joining a car co-op or buying a used Prius. I just looked up on Craigslist and immediately found 2008 Priuses for less than 15k. (I even found a 2009 Prius, but it looks shady). A 2006 Prius, I found for 5k, but it seems like a rare catch.