My little chihuahua boy had undescended testicles. I got him at 16 weeks old and the vet told me that they might still descend if I massaged them down!! I massaged that little boy for a few weeks, to no avail!! But he loved the massages, typical boy!!
I had him neutered and I think it cost me about $250. He has not had any health problems or anything associated with it. Good luck with your new boy!!