Hello, man!
It is really hard to estimate the price of rare items, since their rarity is pretty much variable from server to server.
Since it is a opt-pvp and green server, I'm assuming there aren't many on the server, so I'd say you could get up to 20~25kk on one. But if you're trying to sell it (or buy) I think the best method is to open an auction (in case of selling), putting a minimum price you'd guess acceptable to sell or announce it on your world board and put the offer on market (in case you're buying).
Hope I helped you a little bit