What are some cool cheap b-day party Ideas for the summer?

I have a summer birthday, so lots of ideas. You don't state whether this is a child or adult, but how fun to be an adult and have a child birthday party.
Create a tropical paradise in your own backyard, Big & Little girls will love a Hula Girl Party! Transport your guests to a tropical paradise with elaborate decorations; palm trees, grass table runners, tropical scene kits and tiki lights. Or, simply create a tropical mood with table coverings, a fresh tropical fruit centerpiece and music. Include a surfboard by the entrance and a warm "Aloha" greeting as your guests arrive...don't forget to pass out Lei's!
Do-it-yourself party decorations are possible with some creativity. A refrigerator box can be transformed into a tropical scene using poster paint to paint simple objects...a few palm trees, sand and a blue ocean will do. If painting it yourself isn't possible, enlist a talented teen to do the job.
Cover a table with green butcher paper and fray the edges to resemble a grass skirt. Mount a few travel posters on the walls and hang garlands of homemade tissue flowers (tied along green ribbon). Set the mood with Hawaiian music or the Beach Boys playing in the background. Voila - it's a paradise! For a beach party in the back yard,  create a sunny beach atmosphere. Try just a few ideas, or go all out!

Create your own mini beach by filling a wading pool with sand and sand toys. If you already own a sandbox, use that instead. Build a simple sandcastle and leave sand toys for the guests to play with later. Scatter lots of beach balls throughout the yard or hanging from trees, and hang extra bathing suits on a fence.
If you have a swingset in your yard, put a wading pool full of water at the bottom of the slide and place a hose at the top so that water is running down into the pool as the kids slide down.
Decorate your garage door to resemble a beach scene. First draw various parts of the beach on poster board and then attach them to your garage door. Include the ocean and some sand, plus a surfer, a dolphin or a shark. You could even cut a surf board shape out of cardboard and lean it against the door. Use sidewalk chalk to draw giant letters spelling out “Beach This Way” and an arrow pointing to your yard.
Fill the yard with beach umbrellas, lawn chairs, and beach towels. Add a sand pail filled with a few bottles of sunscreen, and play fun beach music on a portable sound system. Give each guest a flower lei as they arrive.
Balloons always say “party” to children, so tie groups of helium balloons together and anchor them in place with balloon weights.. Or you might like balloons shaped like a fish, a shark, or a pirate’s treasure chest. If you’re serving food indoors, tie a balloon to the back of each chair, and tie a group of five balloons to the birthday child’s chair!
For table decorations, use seashells, starfish, snorkel masks or sunglasses.
Hang a colorful piñata that matches your theme as a decoration. Later it will become an activity when the kids break it open. Consider a pull-string piñata if you are inviting young children.
Make a banner that says “Welcome to [child's last name] Beach” and hang it near the party entrance.