A lot of installers use HV cable with cat5e built into it for the CT clamp or to run ethernet, so it’s just one cable this stuff is pretty expensive. My installer just cable tied a single pair cable behind the 240v cable back to the consumer unit you can’t even see it doing so knocked over £100 off the bill. Might be different now this was nearly 3 years ago Standard install is up to 10m of cable and no more than 2 walls between the EV location and your consumer unit or meter whichever is closer. I found numerous companies some wanted over £1500 to install with a 10m run, one wall just because our meter etc is upstairs even though it’s all on the same wall EV point, meter and consumer unit so it’s one hole cable run done. Eventually I had an epic company Greenvoltz do the job and Motability paid after BP dropped the ball about 10 times. All I can suggest is keep shopping about try to get quotes from someone who’s going to come look first not just give you a figure
Why would they need Cat5e when the charger isn’t going to be connected to the internet?