We are not sure if the EORI must be obtain from the country the supplier is based in you are dropshipping for.
However, we do know it is possible to download a form from the Customs website in Spain, specifically for those people in need of a Spain's EORI number who are not established in the EU,
Link hidden: Login to view ... n_UE.shtml
However, the website mentions you would need to present this form in person in any of Spain Customs Offices, or have a representative do this for you; maybe this is why Spain Customs informed you the cost was 1000 EUR: their fee for the service.
Another useful page in Spain's customs website (please use google translate),
Link hidden: Login to view ... ORI_.shtml
We hope we were at least of some help. We are not experts, so please do make sure all is correct before proceeding with any paperwork or negotiations.