TMZ's got the receipts, and although no one will give us a straight answer as to why certain costs have swelled from prior years, it appears the cost jump is related to Trump's hopes for a massive crowd. 

For instance, according to federal procurement docs ... 2 separate payments of $31,764.24 and  $9,534 were made to a Maryland company for portable toilet rentals. This is roughly 4 times as much as what was spent last year for the Independence Day celebration's sanitation services.

Why so expensive? No one from The White House is talking, but it seems there will be more toilets to accommodate the estimated crowd. If the estimate turns out to be unrealistic, there will be a lot of empty toilets ... except for the taxpayer money that will be flushed down the hole.

We've also uncovered purchase orders of $19,282 to rent golf carts. There weren't any golf carts last year. 

As for the main attraction -- the fireworks -- the USA's forking over $320,549.26 to Garden State Fireworks. That figure swelled from last year's cost -- $270k. 

These amounts are relative peanuts in the world of government, but it's a sign this ain't gonna be a cheap celebration. 

The Prez has promised to showcase "the strongest and most advanced Military anywhere in the World" with "Incredible Flyovers" and has poo-pooed the cost ... suggesting fuel is the only expense.

However, this doesn't take into account the cost to operate the planes and military weapons used throughout the event, and it's been reported the National Park Service is diverting $2.5 MILLION in funds to pay for the July 4 extravaganza.