Think outside the box. A cocktail party is simpler to put together than a dinner, never-mind less expensive. Go for a few simple appetizers - I love to shop at the farmers market where the produce is far less expensive and the the quality is great. A simple Caprese salad on a skewer makes an appetizer that everyone will talk about.
Keep your cocktails to a minimum, and everyone will love tasting a fabulous new wine you found for under $15. a bottle! My favorite wine shop is Brix Wine Shop in the South End of Boston, they have all the greats, but can point you in the direction of some amazing affordable bottles.
When throwing a cocktail party the points that I think are the most important are:
Guest list: People that will mix and mingle
Music: A fun playlist that will keep everyone awake and enjoying the tunes while not taking center stage. I love the Hotel Costes series, as well as the Verve Remixed series.
Cocktail: Make a fabulous seasonal cocktail that everyone will like, then jsut back it up with a coupel simple mixers (think vodka, gin, cran, and tonic) along with wine and perhaps a sparkling you are good to go.
Decor: Simple is best - people will be mingling and chatting, so make one or two larger statements with your decor budget, maybe a large flower arrangement then lots of candles. People will notice one larger rather than ten smaller things.
These ingredients make for a fun and high energy party without breaking the bank!
Cheers!
