Most of Rubino's stuff starts at about $800+ for just a very plain cue. Chances are it would be worth at least that, depending on condition. Depending on documentation/condition/etc.... It would probably go up from there.
Best suggestion, contact Rubino directly. He had a part in the first 2 blue books, and he made the cue, he would be able to tell you (1) what the cue originally sold for, (2) an estimate of the current value of the cue (3) and if you push, a letter of authenticity stating he made it, where he got the "Rambow" forearm, etc.
