London to Ibiza is roughly 800 nautical miles and about two hours in the air, within range of every jet class. It is also the most violently seasonal route in Europe: the same aircraft on the same leg can differ by more than half between May and August.
Private jet charter from London to Ibiza starts from $11,500 on the smallest suitable aircraft. That is an indicative starting price, not a quote: the figure for your trip depends on which aircraft are available, where they are positioned and the date you fly.