Re: Of all time?
Maybe on that side of the pond. The US has multiple Northrup B-2 Spirit "Stealth Bombers" designed for a first-strike nuclear capability over Russia, at a cost of over $737,000,000 per plane (over $2,000,000,000 per plane lifetime amortized cost) and $135,000 per flight hour to operate (and more than double the prep time per hour of flight time compared to other bombers more suited to conventional weapons roles).
Meanwhile most bombs are dropped by fighter/bomber aircraft for smaller sorties or by the B1-B (rescued from a cancelled project because of the cost and time overruns of the B-2) or the B-52 (flying since 1952).
The total program cost for the B-2 as of 1997? Around $45,000,000,000 in then-current dollar valuation.