The costs related to tree surgery/being a arborist are eye watering if you're legit and doing it legally, the insurances needed alone account for much of quotes price. Then having a proper place to dispose of chippings, logs, leaves and debris can add up too.
I was an arborist, still technically am as the knowledge I gained stays with you. I had family who ran the business and he was putting in 80+ hours a week, pretty much any time not on a job, he'd be out putting in quotes for other work. His salary was good at close to £40k but when equated to hours worked, it's a thankless job and works out less than a lot of low skill labour.
Of course you've got cowboys who will do the work at cheaper prices but most of them don't have the liability cover and if something goes wrong, you're going to have damage to property and a nightmare to claim anything without years through courts. They'll also most likely fly tip the rubbish afterwards.
I can't stress enough, anyone getting significant tree work done, ask for proof of cover, the moment anyone quoting becomes cagey over this, dismiss them.
As for danger as an arborist, i've seen some pretty nasty injurys on competent and well trained climbers, it's very easy to miss something as simple as 'included bark' and have a tree stem split on you.