150 F-35s: The Pentagon's most expensive weapons program features jets that cost $159 million a pop.

Twitter: Some projections of the short-form social networking site's value after its IPO exceed $20 billion.

5 Large Hadron Colliders: The most powerful particle accelerator, which made last year's discovery of the Higgs boson possible, cost $4.75 billion to build (but it costs another $1 billion annually to operate).

13 Weeks of War in Afghanistan:  The United States spent $91.5 billion on the war in Afghanistan in fiscal year 2013 -- that's $1.76 billion a week.

Half a Warren Buffett: A little less, actually. The investment guru's net worth is $58.5 billion.

El Salvador's Economy:  The country's entire GDP last year clocked in at $23.86 billion.

Iceland's Economy, Doubled: Icelandic GDP for 2012 was $13.66 billion.

2 Aircraft Carriers: The cost of the newest U.S. carrier, CVN 78, which has been in production since 2008, is $12.8 billion.

6 Freedom Towers: One World Trade Center isn't the world's tallest skyscraper, but it is the most expensive, costing $3.8 billion to build.

16 Burj Khalifas: The world's tallest building was significantly less expensive than Freedom Tower: $1.5 billion.

9 Multi-Year Mars Exploration Missions: The Mars Curiosity Rover and Science Lab mission (including development, rocketing to Mars, landing, and rolling all over the Gale Crater) cost $2.5 billion.

14 percent of the Marshall Plan: The United States dedicated $17.6 billion to Europe's recovery in 1948. Adjusted for inflation, that comes out to $165.59 billion today.

100 Louisiana Purchases: The United States paid France a cool $15 million for the Louisiana Territory in 1803. Even after two centuries of inflation, that's just $226 million.

15 Buckingham Palaces: The fanciest digs in the world was appraised at $1.56 billion by Britain's Nationwide Building Society last year.

1.75 Man-Made Island Paradises: The World, the failed effort to build a luxury private island complex in Dubai, cost $14 billion and was comprised of 300 islands dredged up off the Emirati coast. 

A (Theoretical) Nuclear Fusion Reactor: American and European scientists are trying to develop that holy grail of energy production: a fusion reactor. Optimistic assessments project technology could be advanced enough to build a fusion facility for $20 billion -- 15 years from now, maybe.

5 percent of the Starship Enterprise: Yes, the one from Star Trek. Raw materials, labor, computers, weapons, propulsion, and crew would come out to a whopping $479 billion.

0.000000028% of the Death Star: The Enterprise is a bargain compared to the Galactic Empire's behemoth space station, which economists at Lehigh University estimated would cost $852 septillion. (It looks like this: $852,000,000,000,000,000.)

15 Iron Mans: That's eight state-of-the-art armored, weaponized, flying suits and a playboy billionaire lifestyle (Malibu beach house and luxury cars included), at a cost of $1.6 billion -- 15 times over.

120 Hope Diamonds: The Smithsonian centerpiece, a whopping 45.52 carats, is worth $200 million.

Half the Beijing Olympics: New airport terminals, sports stadiums, hotels, staffing -- the whole shebang set China back an estimated $42 billion in 2008.

Two London Olympics: The Brits got a comparative bargain in 2012. Those games only cost $14.42 billion.

The Apollo Space Program: The two-decade effort to put men on the moon cost $25.4 billion -- in the 1960s. Adjusted for inflation, the program racks up a $150 billion check.