The cost of having the chip inserted will depend on your vet. the one near us charges $65.00 but pays the fees with Home Again for you. The insertion only is about $35.00.
The store I work in puts them in or puppies for $24.99 and the owner pays Home Again fees. A one time acctivation fee of $10.00 and $14.99 a year regstration to be able to locate you if your dog is found. That also includes a lost dog alert that is sent out to ALL vets and humnue society if you report your dog lost or stolen.
And yes it is less then what we spend on clothes and toys and treats for these guys.
I have put the chip in puppies as young as 8 weeks and under 2# and it doesn't hurt any worse than vaccines. Some never even notice it's being done. The chip is like a long grain rice. a little bigger around but not huge.

It CAN NOT be removed without surgury. so I don't think someone stealing your dog is gonna try to get a vet to do it. Worse case they try to cut it out and I don't want to think about that. Most never take them to the vet to check to see if they have one. They would sell the dog to someone else who would end up at the vets office and be told the puppy is stolen. and you would be contacted and the new owner would be out his/her money AND puppy. But they should know to buy from breeders they trust.