Saffron: £10 per gram

The most expensive spice in the world, saffron costs between £5 and £10 per gram at the supermarket. 

The spice is so dear because the process is labour intensive. Each flower produces just a few stigmas, which need to be hand-picked and dried before used with food. It can take around 150 flowers to produce a gram of saffron.

Iranian beluga caviar: £20 per gram

The eggs from this rare sturgeon generally cost about £20 per gram and have been dubbed by the Guinness World Records as the most expensive food in the world. 

Platinum: £23 per gram

In 1976, the Recording Industry Association of America introduced the platinum certification for records that sold more than one million units. 

However, at £23,144.63 per kg, or just over £23 per gram, platinum is currently less valuable than gold.

Gold: £28 per gram

Gold has slipped from its 2011 high of £37.31 over recent years, but a rebound this year has taken the price back up from its £22.37 low in August 2015. 

Heroin: £55 per gram

One hit of heroin would likely be anywhere from 10mg to a few hundreds mgs. But by the gram, heroin is among the more expensive drugs, costing around £55. That compares to £46 for a gram of cocaine, £39 for a gram of ecstasy and £13 for a gram of speed. 

Rhino horn: £69 per gram

Rhino horns can fetch up to $100,000 per kg, or £69 per gram. Poaching has seen a resurgence since 2008, after a rumour spread that rhino horn powder had cured a Vietnamese politician of cancer and amid growing wealth in the Southeast Asian country. 

White truffle: £222 per gram

In 2010, the most expensive Alba white truffle ever sold, weighing 1.3kg, went to Macau billionaire Stanley Ho for $417,200, meaning he paid $320.92 per gram. 

However, presumably less superior Alba white truffles can be bought for around £3 per gram. 

LSD: £2,085 per gram

The most common form of LSD is a small square of paper that melts on the tongue. At around $5 for a hit of acid, that adds up. A gram of LSD in crystal form can cost around $3,000. 

Plutonium: £2,763 per gram

The nuclear substance goes for about $4,000 – probably why Doc Brown had to steal his, to keep Flux Capacitor running costs down. 

Postcard: £5,293 a gram

The most expensive postcard in the world –sent from a Fulham-based writer named Theodore Hook to himself in 1840 – was sold for £31,758.75 in 2002. Considering its weight, Latvian collector Eugene Gomberg paid more than £5,000 per gram for the world's oldest postcard.

Soliris: £10,500 per gram

Soliris – believed to be the most expensive drug in the world – treats a rare, life-threatening disease called atypical Haemolytic Uraemic Syndrome (aHUS), which affects the kidneys and vital organs.

A year's treatment of Soliris in the UK could rack up a bill of £340,200.

A 300mg vial of Soliris costs £3,150, which equates to a per-gram cost of £10,500. 

Tritium: £20,748 per gram

Now that you know tritium costs around $30,000 per gram, you might take a bit more notice of the self-illuminating exit and emergency signs which contain the substance. 

Diamond: £45,000 per gram

The most expensive diamond ever sold was the Pink Star, a South African gem that fetched £51.7m in 2013, working out to £4.38m per gram. At 59 carats, the nearly-12g oval diamond measures 2.69cm by 2.06cm.

However, a less rare, colourless 1-carat diamond goes for around £9,000 per carat, which equates to £45,000 per gram. 

Stamp: £5.6m per gram

The 1856 British Guiana One-Cent Magenta postage stamp sold for £5.6m in 2014, making it both the world’s most expensive stamp and, at just 2.5cm by 3.2cm, the most valuable object by weight and size.

Californium: £18.7m per gram

Californium can be used to start nuclear reactors and treat cancers. It is also found in metal detectors. But at $27m per gram, you'd have to be finding some pretty precious metal. 

However, there is, actually, one thing that is more valuable than even this...

Antimatter: £17bn per gram

In 1999, Nasa said it would cost $62.5 trillion to produce a gram of antihydrogen. Seven years later, it was estimated that a gram of positrons (the antiparticle of the electron) would cost $25bn to make. CERN has spent a few hundred million Swiss francs on producing a billionth of a gram – which would put a gram at a few hundred quadrillion francs.