I had to have mine moved as part of my renovations. It’s the most over priced con ever ever experienced.
Assuming the existing gas pipe is a plastic one and will reach to the new location it basically a fixed charge to include digging the hole, putting the pipe into the meter box and connecting to the meter then making good the hole.
The meter box is expected to be installed ready to go. They will not connect or test the connection to your side of the meter. Nor will they turn the gas on, you need you gas guys to do that.
So it’s basically ~£750 for a couple of hours work at best. and as for the whole “making good”…. pah.. lucky I was planning on resurfacing the path anyway!