It vastly depends on how common your material is and how liquid.
RedBook is typically 12-18 months out of date (the 2020 book went to press in 1Q2019 and has been for sale since the end of 2Q2019)... And at best the prices are high (full) retail.
PCGS' site (and NGS' also) are for their own plastic and IMNSHO they are a little proud of their plastic.
Since any fool can purchase the greysheet, the game becomes dealers paying less than greysheet to buy so they can sell at greysheet and still make money. This peaked just before the new owners took over and raised the price of the greysheet and did away with the single-copy sales. But you can still get your hands on a current or month-old copy without much work...
-----Burton
50+ year / Life / Emeritus
ANA member (joined 12/1/1973)
Life member: Numismatics International, CONECA
Member: TNA, FtWCC, NETCC, EveryCountry (online) coin club
Owned by three cats and a wife of 40+ years (joined 1983)
Author: 3rd Edition of the Sample Slabs book,
https://www.sampleslabs.info/