I see five 330i ZHP's currently for sale online (all apparently in very good to excellent condition--like your car) with the following mileage and pricing:
2004, 53k miles, $23,000 (dealer)
2005, 54k miles, $23,000 (dealer)
2003, 60k miles, $22,000 (dealer)
2005, 106k miles, $15,000 (dealer)
2005, 128k miles, $13,000 (private)
So, I would think you'd ask $17,000-$18,000 for your car with 77k miles. She is a beauty!
2004 BMW 330i ZHP (52k miles), Jet Black with black leather, MFactory LSD (3.38) with Z4 cover, 18"x8.5" ET38 APEX Arc-8's (Anthracite) with 245/40 Michelin PSS', Koni Sports with factory springs and front and rear reinforcement plates, Shark Injector, Corsa TSE3 cat-back exhaust, TMS under-driven pulleys (water & steering), CDV delete, TMS CF strut brace, K&N CAI, GAS DISA rebuild, TMS pedals, Wheelskins steering wheel cover, roller tray center console, black-out grilles, and WeatherTech mats