Although I think my husband was ripped off( he went to a different dentist) the charges where I go are reasonable.
checkups are free, with clean and polish- 25 euro.
Small filling 30 e, large approx 50 , and they are white fillings.
Unless it's a front tooth, fillings on NHS will be amalgam , so you can 't really compare .
you have to compare like for like,so don't compare Spanish private with UK NHS as they are not the same, both in quality or prices.
As for not being unable to get an NHS dentist, where I used to live, NHS dentists were advertising for patients!