Nope, i don't know how much a lambda sensor is the a freelander but i replaced one on my polo recently and it was £55 i think. Eurocar parts seem to do 30% off every weekend, so worth checking there.
Also might be worth checking all the pipes around the engine, the polo had an error code which caused me to replace the lambda but it was actually a cracked pipe for the crank case breather causing the car to run lean.
In terms of replacing, they just screw in and plug into the ECU. id recommend buying an actual one for your car with the right connector and not a universal one, and don't buy budget.