Trying to follow this example 100 wei seems very low for the gas price. Is it using a different unit? I'm also slightly unsure if the value should be hex or decimal, or if it accepts both
On the main github page, the value
0x09184e72a000 is used. Converting that to base 10, we get this figure: 10,000,000,000,000 (10 quadrillions).
According to the gas station, we can consider the average price (as of May 2018) to be 12 gwei, or 12,000,000,000 (12 billions) wei.
We can thus deduce that the amount set my
ethereumjs-tx creators was set in wei, so that your contract will always have enough gas. They also perhaps assumed you'll be using it on a testnet first.