A benefit party this Saturday capping American Cinematheque's 18-day Rock on Film festival at the Wiltern Theatre has been canceled, a victim of "escalating costs," organizers said Monday. Although more than 300 ticket holders had shelled out $100 for the event, Cinematheque Artistic Director Gary Essert said he realized last week that a catered reception and live band would be too expensive: "Costs involved logistics--the stagehands, the theater itself, the presentation of food all affected the other." However, Essert added that the Cinematheque has no financial problems. Ticket holders may opt to put their $100 toward the American Cinematheque Moving Picture Ball in March ($250 a pop) or receive a refund. The Los Angeles premieres of "Jimi at Monterey" and "Shake" will screen Saturday as planned, along with a midnight screening of "C-S Blues," rescheduled from Jan. 2. The festival has suffered from several last-minute film cancellations and reschedulings as well as sound and screening problems. Essert's response: "It goes with the territory. When you put together something this complicated with material this old, things happen."