That southern border wall Donald Trump said Mexico would pay for? Well, it'll probably cost the American taxpayer at least $4.1bn (£3.3bn) to finish.

That's how much President Trump reportedly plans to ask for from Congress over the next two fiscal years to fund the controversial wall, though a leaked report by the US Department of Homeland Security suggested the final cost to the taxpayer could actually exceed $21bn.

"I will build a great wall," Trump promised in a June 2015 speech.

"And nobody builds walls better than me, believe me. And I'll build them very inexpensively. I will build a great, great wall on our southern border, and I will make Mexico pay for that wall. Mark my words."

The wall will stretch along America's border with Mexico. The White House has stipulated it must be "physically imposing" and 30 feet high, very difficult to break through or tunnel beneath, impossible to climb without a ladder, and "aesthetically pleasing in colour" on the US side, ideally blending with its surroundings.

Is it really worth it though? Is the flow of illegal immigrants at the border that large or problematic? Couldn't the $4.1bn be better spent elsewhere? Here are a few suggestions for President Trump.

Help struggling public schools.

Many American schools have budget deficits because of cuts to education spending with poorer areas, where money is needed most but in shortest supply, particularly affected. They desperately need repairs and new equipment, but can't afford to pay for it.

The school system in Baltimore, for example, where around a quarter of residents live below the poverty line, has a $129m budget deficit. That $4.1bn could go a long way to improve school infrastructure in the worst areas.

Buy a massive luxury yacht.

Trump has all the charm and taste of an ostentatious nouveau riche oligarch. So why not commission the most expensive luxury yacht ever built? What could make America greater than a gold-plated, jewel-encrusted, high-tech superyacht that every American is able to use?

There would be around 324,730,000 Americans eligible to use the superyacht called "Sea Force One" or "Mayflower 2.0" or something. So every year, each American will be entitled to have it for approximately 0.00000112401 days. Happy sailing!

Give every single American $13.

Go buy yourself something nice, like two Big Mac meals.

House homeless veterans.

According to the National Alliance to End Homelessness, there are around 50,000 homeless veterans living on America's streets. Many need mental health support to heal the psychological wounds of conflict. Around three-quarters of homeless veterans have a mental or physical disability.

Some programmes to help end the problem of homeless veterans have seen success. For example, in 2015 New Orleans announced that the city no longer had any homeless veterans. But there is clearly still work to be done across the country, and that work needs money.

Invest it in the Trump Organization.

Trump's family is using the White House as much as they can legally get away with to cash in on the presidency. Trump himself frequently uses his own Mar-a-Lago resort in Florida – which he calls the "Winter White House" – for official businesses.

And if you can't beat them, join them. American taxpayers should get Trump to invest the $4.1bn into his own company so everyone can reap the returns of his family's shameless efforts to make bank from the White House.

Fund the start-up costs for unemployed Americans to set up their own businesses.

The unemployment rate in America is 4.7%. Many Americans who are employed are stuck in low-pay jobs. To help improve the lives of those at the bottom of the pile, who need a foot up in life, Trump could direct the billions he would spend building the border wall towards government grants for the unemployed and low-paid who want to set up their own businesses.

The money could fund the start-up costs for those with a viable business plan but who don't have the means to get going. Not everyone can inherit a fortune like the president did from his father.