ADVICE required on the best cloud service for our needs

- we have multiple clients that run our software (about 100) - we would like a secure cloud service to run on the clients PC where they can drop image files into a folder (with further sub-folders), also delete files, move, copy. - we want these images to sync and appear on our PC (which is running advertising software) - in affect, the client chooses the images that run on our advertising machines - the client will have their own permissions to access their cloud folder - we will also have full access via permissions on our advertising PC - our clients are small not-for-profit organizations, so ongoing costs will be a factor There are too many cloud service options out there - we need assistance. Is there such a cloud service that we can purchase and manage multiple accounts on? Under the 1 controlling company name? We NEED an expert to point us in the right direction. Please submit your fee & expertise, for successful consultation of this task. Thanks