Plant catnip well away from your gardening area? My sister has barn cats and she does that. The population of the cats seems to have natural controls as there never seems to be more than a dozen or so. Personally I would spey or neuter but that could/would get cost prohibitive I suppose.
Look for low cost spay and neuter clinics in your area. Here they literally do 1000’s of animals a day. Feral ones are done no cost. Staffed by a bunch of libs (aka Fake Americans) , but good at their jobs. A vet can spay 10 animals a week vs. 200 a day.