Dentists are often able to get toothpaste from manufacturers for really cheap, since the manufacturers hope the dentist will give it to their patients (and thereby implicity 'endorse' that brand of toothpaste).. . You should try to hit up your dentist. Perhaps he or she will contribute toothpaste to your organization (something really inexpensive). In return, your organization can make it a point to give that dentist some kind of recognition for the contribution (mentioning it in a newsletter or something).