Someone is always stealing from our yard and now breaking into the cars?

I've lived my house for about a year now and whenever anything is put outside, such as holiday decorations and lawn ornaments, potted plants - they are stolen.. or usually they take all but always leave one of whatever it is. Made police reports but there is nothing they can do since we never catch them in the act. Last night my husband came home late from work and forgot to lock our car, someone got into it last night but looks like nothing was stolen since he doesn't keep much in there. Ashtray was pulled out and there was things moved around but that was it. I can't afford some expensive camera to put out there, police can't do anything so what else is there to do? Maybe set some trap, if so any ideas? It's getting really annoying and we can't have anything in the yard. It's a pretty good middle cl neighborhood and I'm not going to move. I suspect it's the same person/people.