Free mastiff puppies are not widely available, but rescues sometimes have very affordable mastiffs for adoption. Rescues may also occasionally waive their adoption fees, although this usually only happens at certain times for promotional reasons and may not coincide with the availability of mastiff puppies.
Most breeders charge a significant amount of money for mastiff puppies, because they put a lot of money into producing those dogs; for example, the mother and puppies need veterinary care during the pregnancy and before the puppies are old enough to go home, and breeders often show the parents in dog shows. Some owners may find themselves with accidental litters and give the puppies away for free, but puppies from such litters may have health or temperament problems. Mastiffs are large and naturally protective dogs, so a good temperament is particularly important in this breed.
Most shelters that have fee-waived adoption specials promote them on their websites and may even contact local news organizations, so people interested in free puppies should check regularly. There are also some organizations that may help subsidize adoption fees, so adopters can try contacting them. However, adoption fees are usually the least expensive part of owning a mastiff. These large dogs need a great deal of food, training and veterinary care throughout their lives.