In 2017 the federal government spent 4.147 trillion dollars.
https://en.wikipedia.org/wiki/2017_United_States_federal_budget
The 5 billion is 0.0012% or a bit over one one thousandth of a single percent of what was spent in 2017. To reach even one percent of the total expenditures spent in 2017, Trump would have to get 414.7 billion for his wall.
so this fight has become a matter of principal, not of substance when it comes to spending. Strange as it may sound, the Democrats were all in favor of building a wall back in 2006 and voted for it. Even though that legislation passed and was signed into law, it was never funded. Hence not built.
The wall in my opinion has taken on a pro vs. anti Trump stance than whether or not it has merit and could help the illegal immigration problem. It's 100% politicized. Hate Trump, be against it. Love Trump, be for it. This whole thing is 100% very partisan BS. When you only talking about one one thousandth of one percent, it can be nothing else but partisan politics at its worst.