I'd spend as much as neccasary.

I paid $630 for two tickets to stand dead center 2nd row to see Jack Johnson, Willie Nelson, Ben Harper & ALO in Hawaii this April. Normally I'd cap that to around $150 for a festival but this all went to the Kokua Foundation of Hawaii, so I didn't mind it.

You guys/gals should check out the Beale Street Music festival, its the first weekend of may every year. Costs $48 for 3 days of music. Well worth the 5 hr drive every year.
Memphis In May

I got to experience BB King, Robert Randolph & The Family Band, Puddle of Mudd, Jason Mraz, Cake, Huey Lewis & The News, George Clinton, Jerry Lee Lewis, Gin Blossoms, Yonder Mountain String Band, Blues Traveler, Chicago, Govt Mule, & Galatic this year for only $48.

Last year I got to jam out to Jack Johnson, Trey Anastasio, Ozomatli, Nickel Creek, Michael Tolcher, Los Lonely Boys, Jerry Lee Lewis, K.C. & the Sunshine Band, Spin Doctors, Particle, Tesla, The Black Crowes, Billy Idol, Robert Randolph and the Family Band, Elvis Costello, The Roots, Billy Idol, & War.

I've been 5 years running and don't plan on stopping anytime soon. Need to age some nice smokes for 2007!