You have the greatest input needed with costume ideas and that is, your ideas. You do not really have to buy or rent a costume if you do not want to. You can use your own innovative ideas and make a completely unique costume. The first step is to know about the situation. You would not want to have some glittering and jazzy costume for a formal dinner. On the other hand you do not want to dress professionally and formally for a hip party.
If you are going to a custom party or ball you can let your imagination run wild and have fun with your costume idea. You can go as Pinocchio and have a cardboard pencil nose tied with a skin or white coloured elastic band. If you are a heavier built person you can pain yourself blue and go as Genie from Aladdin. However, if you are going to a ball that needs periodic style costumes you can choose your favourite person in history and dress as them.
Innovative, creative and imaginative are the key essentials to creating a fancy dress costume. Have a good look in your wardrobe for everyday clothing that you can use. A baseball themed event can have you posting a hilarious slogan on a T-shirt. You can dress up quite easy as a klutz by wearing mismatched clothes or odd socks.
Have you ever tried playing with watercolour tubes that your kids may have lying around? You can take these and dress your kids in a regular shirt and pair of shorts and draw a moustache and put a hat and holster on them. Then just enjoy how much they love their new looks. Costumes can have a great impact on the people who see them on you. If you are addressing an issue, try using a costume to get people's attention and draw them into what you are trying to say.
If you want kids and adults to learn more on genetically modified foods, dress the little ones like a tomato and tell them what are the pros and cons of the foods. The kids and grown ups would love to remember the information rather than going through a boring textbook.
Costume ideas can be a true representation of you and your personality. If you are a huge fan of the 1970s then make up a costume that will reflect that era of Glam Rock and Disco. If you have a wild and wacky personality then choose something that will reflect that. You can plan costumes for virtually any occasion. Make an impression and design your own unique costume rather than resorting to expensive ready made ones.