We have also been looking into providing some form of RF tagging for equipment maintained by avensys engineers >75000 devices and rising. The cost is still too high, however, I have been following companies involved with RF harvesting and associated tagging
www.rfenergyharvesting.com. This gives you an insight into the technology or not? It sounds feasible but I have yet to find any such device on the market, but I am sure they will get there and if they do and soon then cost should reduce quite drastically.
