I've unfortunately had to have two dogs put down over the years, and both were at different vets in different counties but still same general cost of living. Both were a little over $300, I can not remember how much extra the cremation was for the first one (my dog). We did not have the second dog cremated, it was DH's heartdog and he didn't want him cremated. But the cost of the euthanasia was still over $300.
We are not in a high COL area, I would say it's midrange. I would imagine you could find a lower cost vet somewhere to do it for under $200 unless you are in a high COL area. It may not be your usual vet though. Often shelters will do low cost euthanasia's, but I have no idea if they have cremation services available to them or not. There are probably private services that will do it, but I would think it would be $$
Also, regarding cremation - you can opt for group cremation (with other animals) or private. Private will of course be more $$, but personally speaking when I had my dog cremated, I wouldn't have done it if I couldn't do private, because I couldn't imagine just having various dogs ashes in the urn.