The vast majority of things that can go wrong with you in Spain are covered by your EHIC (if you've got one that's still valid) or your GHIC. So, if you break your leg or end up hospitalised for weeks, the insurer possibly won't have to pay out anything at all. The 'health' element of your insurance really covers little more than the cost of flying you home in an air ambulance if that should be necessary.
However your EHIC/GHIC doesn't cover you at all in the Dominican Republic. So if you're hospitalised for a couple of months, your insurer will have to pay out a fortune. Hence the higher premium.
Even so, unless you're particularly old or have serious pre-existing medical conditions, you seem to be getting quoted unusually high premiums. The last time I took out travel insurance was about three years ago, when I took out ANNUAL European cover (at the age of 66) for just £16. So £110 for one short trip to Spain sounds ruddy expensive to me!
This is the company that I used:
https://www.holidaysafe.co.uk/