The costs of TNR versus trap-and-euthanize will vary greatly location by location and an individual analysis of your community will need to be done if you want accurate results. Also remember the question is not just what are the costs, but what are the costs to the municipality or shelter? We tend to think of volunteer work as "free", which it is to the municipality or shelter, but not to the people doing the work.
So if the question is what are the comparative costs to the municipality or local shelter of TNR vs. trap-euthanize, here's what to consider:
Costs of trap-and-euthanize may include all or some of the following: the costs of capturing the cat if performed by an ACO or other municipal employee (labor, fuel, other vehicle-related expenses), the staff time (labor) required at the shelter for intaking the cat, the staff time for caring for the cat during any mandatory holding period, also food, litter, etc., during the holding period, the cost of the euthanasia procedure and the cost of disposal of the body. Some shelters will have performed this analysis already and know the per cat cost.
Costs of TNR may include the costs of capturing the cat (while usually this is done by volunteers at no cost, an increasing number of shelters now employ community cat staff), the cost of the spay/neuter surgery and any required ancillary care such as vaccinations, the cost of any staff time taking care of the cat pre- and post-surgery (again this is often done by volunteers) and the cost of transporting the cat back to his colony site.
In my experience, in most communities, the bulk of the labor and expenses for TNR are born by volunteers and nonprofits, while the costs of trap-euthanize are entirely borne by the municipality/shelter. So under this framework, TNR usually ends up costing the shelter or local government less.
Hope that's helpful!
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