Cost example, I have checked that I'm allowed to share and what I can share for GDPR reasons so this may be a bit vague.
Location, Tenerife
Activity, Hiking
Injury, Minor Head Injury, slight concussion, broken left leg, fracture to ribs.
Treatment, x-rays, MRI, plastics and surgery, cast, general monitoring.
Duration of Hospital stay, 11 days
Medical Treatment Cost, £16000 (rounded to closest 1000) this is quite a bit below average for the length of stay and treatment received.
Cost of Medical Repatriation, £23000 (rounded to closest 1000)
All costs had to be covered by the patient and family as they had taken general travel insurance and not advised they had gone with the intension to spend the time hiking on or off defined trails.
These costs are fairly average, becoming I'll on smaller islands or in smaller countries often sees a patient moved by air, sea and road to a facility which has better equipment or more resources/money which can also bump up costs.
The best thing to do it speak with your insurer, tell them what your going to do, most will amend a policy to include certain activities. It may cost you an extra £100 it that's better than loading credit cards or remortgaging a house.