If the time frame is so short, you may not have much of a chance but to sell the drum kit.

Try selling stuff on Craigslist - You'll have the cash in your hand and ready to spend much faster than Ebay, in my experience. Also, ask family friends if they'd like a babysitter, have their lawn mowed, or hell, even their houses cleaned. You'd be amazed how many lazy-ass housewives will shell out for a little dusting and scrubbing.

Sorry that I can't tell you the secret that makes $500 appear in your hands instantly. However, if you'd like to learn, send a letter to me with a money order for $500. :-D