Cruise Missile $1.5M *each*
Lump of iron $15 *each*

Lifetime and usage costs will always support BFG solutions.
AND what if the "oppenent" was able to stop fuel getting to the owners of Cruise missiles ?

Even if the gun is $10m then it only takes 10 shots to be cheaper than cruise
AND only one item to service and maintain, not every cruise.
Boeing made $40M converting just 90-odd Cruise from normal to bloxck buster. OUCH