We used tires, we have several stations set up with 3 poles from the ground that hold the tires together, that were used for hitting deills and when it rains, we just took them off the poles to weight the tarps down.
I have seen folks use like 4 inch PVC pipes and cut them about 1 1/2 foot lengths, drill holes on both ends to put in PVC rope handles to carry them by, and fill them with quick dry concrete. Fairly cheep but they worked and lasted in all weather conditions...