The Qatar World Cup is the most expensive ever held

Here's the chart:

source

Why so expensive?

Because they built eight new stadiums from scratch, plus a brand new metro system to ferry around fans, new airports, new hotels, they expanded the road system, the works.

Whereas the USA 1994 World Cup was so cheap because they used existing stadiums with no upgrades (they had so many, the difficult part was choosing which to include), they already had a metro system, plenty of private hotels and restaurants etc.

Most countries either use World Cups as an excuse to spend on infrastructure, or to gain global publicity for their countries or both. The USA in 1994 was an exception - it used the World Cup to introduce soccer to their home audience.