A couple years ago for my 16th birtday i decided to have a fiesta. I sent out invitations with a guy dresses like he was from mexico and invited a ton of people. I had over 100 people there. I decided to decorate my back porch.  I took christmas tree lights and place a part of a fake flower over them. I took the fake flower and split it into 4 to 6 pieces where ever they split and threw away the stems.  Those were very inexpensive.  I hung those over top of my porch. I also hung a pinata from the middle of the porch and filled it with candy. I had fajitas for the food and a cook i know made them himself right in front of us on a grill.  I also ordered chips and salsa from a local mexican resturant.  My cake was in the shape of a sombrarro. Those are easy to find.  I also had one of my friends DJ.  Before the party started I took 16 year old pictures with me and 8 of my best friends.  We had a lady i know come over and take pictures with her personal camera she wasnt a professional but it was really cool and my friends loved it.  I also had a picture of me blown up by our local copy center such as kinkos and every one signed it. I still have it and that was a few years ago and whenever i am bored i take a look at it. It was a great party and didnt require much effort