If a MiG-21 is a thirsty option, imagine what Jared Isaacman has to spend each time he takes his large MiG-29UB (formerly part of Paul Allen's collection) out for spin around the neighborhood.
Jet fuel is cheapest here. Maintenance is what is problem. MIG29 is more forgiving. Astro is right. With MIG21 you better be experienced as hell, as that plane killed so many people that it got nickname “flying coffin.” Add to that that airplanes in private ownership as far as I know, cannot have ejection seat per FAA regulations.