answer:The cheapest would be a local junkyard for they will many times get cars which may have been totaled in an accident but various spare parts are left totally intact. As for preventing future theft, you should consider a very sensitive very loud car alarm which would go off the moment someone touches your car. If it were me, I would put the majority of the money into the alarm system otherwise you’re just risking a repeat of the same. Since it’s a spare tire, an undamaged junkyard version should get the job done. At least that’s what I would do, but I’m a thrifty type (and some might even say cheapskate :)