To answer your question I would say between 300 and 600. It really depends on where you live. You have to find a breeder who is fair from all ends, which can be rare. Your dog should get along with the puppy fine as long as he is well socialized.
I can tell you my experiences with breeding Jack Russells and since Fox Terriers are very similar you can surely compare. I have 4 adult Jack Russells. I show my dogs several times a year from Virginia up to Connecticut. I research pedigrees and carefully plan every litter. Just because I have a stud at home doesn’t mean he should sire every litter I have. My dogs are all genetic tested. Jack Russells are prone to deafness and eye issues like PLL and cataracts (Fox terriers probably are also). I BAER test all my breeding stock and CERF my dogs every year.
My last litter I had to pay a $500 stud fee because I thought he best suited my female. She needed to have a C-section which cost an additional $1000.
She had 6 puppies, 5 boys and 1 girl. 2 males have a slight overbite(which may correct itself in the future) but they will be sold for $350 with a neuter contract. I also added that if there is any medical problems due to the overbite (a tooth needs to be pulled or filed down) I will pay up to $200 towards the vet bill. The other two males are show quality and are registerable, they will be sold with breeding rights for $550. The female is $600 and I am keeping a male to show.
If you include vet bills I am paying $2000 for this litter. The most I will make back is $2400 and the least (if I have to refund 200 for each of the vet bills) is breaking even. I am clearly not making a profit, but I love the Jack Russell breed and I am thrilled to have a puppy with such fine bloodlines. And I can’t wait to start showing him when spring come around.
Find a breeder near you.
-Ask how many breeds of dogs they have.
-How many litters a year they have.
-Ask if they could name some popular dogs in the pedigree and what problems follow which lines.
-Ask if they have both parents.
-If they show (or compete in dog sports)
-Why the puppy is that specific price.
-Important is genetic testing. Do they test their dogs and can they show you the paperwork to prove it.
Questions like this to a breeder over the phone will intimidate a “backyard breeder” who is overcharging for a buck in their pocket!