R-6 values vary from one coin to another. A huge factor in value increase is popularity, obviously increasing the demand and the price. Oldgrouchyguy makes a good point, it is a "very rare" die state, but the variety remains obtainable altogether.
Additionally, Parsley's fifth edition of United States Early Half Dollar Die Varieties 1794-1836 lists the O-105a die state as an R-3, the same rarity as the O-105. Peterson's first edition of The Ultimate Guide to Attributing Bust Half Dollars (older edition but can be used as a guideline) shows no extra value for the O-105.
With Dave's Bust Half Dollar Site and Parsley's United States Early Half Dollar Die Varieties 1794-1836 contradicting each other regarding the rarity, I believe the rarity of the die state is not known entirely. The R-6 rating may be neat and provide a "cool" factor, but it won't bring a significant premium.
I give this coin a G-6 and a value of about $65.