I assume you've spoken to an electrician who has experience installing EV chargers and can handle the EV Grant paperwork/application etc?
EV charge points need to be connected to the meter box directly in most cases so if your meter box is at the front of the house and the garage at the back of the garden, which based on your description, it is, then I'm not surprised it's a "big job". That being said, the "big" aspect of the job will be running the supply cable from the meter box to the charge point location (the garage). That might involve groundworks and trenching, or even laying under a patio/slabs etc. Have a look at your garden and see if you can find the least invasive (but safe) route for cabling to be run. Suggest that as an option when you speak to electricians. Most EV installers will to remote or touchless surveys and will simply as for pictures, site plans etc.
I was in a fairly similar situation with my meter being at essentially the "wrong" side of the house so I'm having to get the charge point supply cable run around the rear of the house, along (under) my patio decking, and into the garage, over the inside of the garage door and the charge point mounted on the external pillar. It's around 25m of cabling and overall the install will cost me around £1,100.
I've commented earlier in this thread with my site plan etc. so take a look if you want to get a feel for what I sent to the EV installers. I'm based in Warwickshire so can't recommend anyone in Cornwall I'm afraid.