My replacement key here in San Diego was $250, but I was able to program it myself using my Faultmate. But yes they are custom ordered and laser cut by VIN all the way from Solihull.
See if one of the local independents will program the key for you, that can save a little bit on the price.
Having only one key for an LR3 is a VERY risky situation, because you need at least one of the existing keys working to program more keys. If you can't cough up one of they keys, you have to replace the Central Junction Box (CJB) which is the main brain of the whole truck. It is not cheap nor easy to replace. Even the dealer can't override the security portion of the CJB if you have no working keys.
"It doesn't swoop, curve, or look like it's going fast when it's parked. It never looks like it's going fast. It doesn't go fast
." - Richard Hammond, BBC Top Gear