Actually, tanks are relatively cheap compared to ships and planes. Singapore spends much more for armaments for its air force and navy.

Tanks may not be able to move freely in urban settings, but it could work as mobile direct-fire artillery. Without tanks, infantry can get massacred in cities, just with machine guns placed on windows. With tanks, these machine guns can be obliterated, but infantry must return the favor by eliminating AT teams

So in urban combat....infantry is king, but tanks are still essential for cover and direct fire supports