This is a great idea
IF you've got plenty of other sources of funding.
In my group we loose money on most every adoption - we usually get a couple of dogs each year that have already been fixed and so save that cost. We recently raised or dog fee so that it comes closer to our actual average cost of care - spay/neuter, vaccines, fecal testing, deworming, heart worm testing & preventative, etc.
Maybe one of these times my dogs and I will figure out the right numbers to win the lottery and be able to build a nice shelter for all the cats and dogs in need of new, forever homes in our community.
Until that day we will continue to apply for grants and hold fund raising events to supplement the fees we get from adoptions.