Depends.
Premium BU usually refers to a coin that is above average uncirculated, usually with pleasing (or no) toning and is a bit more subjective than MS-65.
Its possible that something could be advertized as Premium BU but only grade an MS-63 or MS-64 because the scratches/nicks that decrease the grade aren't easily visible on the coin (usually because they are hidden by toning), or a premium BU coin could grade higher than MS-65.
It also depends on the dealer. Some dealers very sparingly use premium BU on coins and the coins that they call premium BU really are the choicest of the choice. On the other hand, there are some dealers that use premium BU all the time and apply it to coins that are average uncirculated.
MS-63 $2.00 in MS-65 $5.00
Current retail value for a MS-63 1927 Quarter Eagle is $910.00 in the grade of MS-65 (Gem BU) is $4,390.00
For a MS-65 (Gem-BU) retail list at about $100.00.
If you mean a 1882cc Morgan dollar in MS-65 retail price is $400.00 to $500.00
If the coin is a Gem-BU (MS-65) grade, retail value is about $20.00, if it's not at that grade level the value is for the silver at $6.50
If your BU is actually a MS-63 coin. Retail value is $30.00
I think you're referring to MS-65. Please see the Related Question for more information.
Retail for 1885 in MS-65 is $200.00
MS 63, MS 64, and MS 65 refer to the grades assigned to coins in the Sheldon Scale, which measures the condition of coins in terms of their quality and wear. "MS" stands for "Mint State," indicating that the coin has not been circulated and retains its original mint luster. The numbers indicate the coin's quality, with MS 63 being considered "choice" but showing minor imperfections, MS 64 being "near gem" with few noticeable flaws, and MS 65 being "gem" with high visual appeal and minimal imperfections.
65*65*8
A CAC certified MS 65 coin is the best way to go. I have seen MS 65 CC silver dollars with MS 65 that looked like garbage.
The value of coins vary greatly with condition. Within mint state (new) coins the condition and value also varies greatly. If the coin mentioned were in fact truly a gem bu. Gem bu being defined as ms (mint state) 65 or better it would be quite valuable. Probably in the $ 10,000 range. If it were choice bu (ms 63) it would be closer to $ 2,500 and if it were just bu (ms 60) it would be valued at about $ 800. Circulated examples vf sell for about $ 200 and xf for $300. Since the value increases so dramatically between ms60 and ms65. It would be just about impossible to sell the coin as a gem bu without it being certified as to grade by one of the major coin certification services. Hope this helps.