Ponchsox. There's no set answer to that.
If it's a common coin with many examples known in all grades, details slabbing will knock 50% or more off the value in a straight grade, say from an XF-45 to a VF-20 price or even lower.
On the other hand, there are some coins such as early
Half Cents & Large Cents, and Bust and earlier silver coinage, where straight graded coins command a substantial premium; in that case, details slabbing might not knock the price down by more than a grade or two. (Feel free to send me all your unwanted Details-slabbed Chain Cents... ;)
In addition, key dates of a coin series (1877/1908-S/1909-S
Indian Head cent, 1909 S-VDB Wheats, 1885/1886/1912-S
V nickel, 1893 & 1894
Morgan dollars) or rare mints (CC coins, gold from Dahlonega or Charlotte) are always going to be in demand even in details holders, so there's not as much of a drop.
Details coins do have a market at the lower prices, mainly with type set collectors who are more interested in eye appeal than original surfaces, and they offer a great way to put together albums with nice eye appeal. Plus, if you've always wanted, say, a Draped Bust Large Cent, a details grade can allow you to purchase a "nicer" coin for less money (e.g. you can get an 1802 Large Cent in F-12 or VF-20, that body bagged for details for light cleaning or slight porosity, for what you'd pay for a straight-graded VG-8 example of the same coin.)
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