I have sold two non running, rust free K5s in the past 3 years. First one was missing all the interior and had a disassembled tcase sold for $3500 in mid 2020. Second one was complete, mostly cleaned up but the 6.2L diesel would not start. Was looking like it needed a rebuilt injector pump. That one sold for $4500 in mid 2021.
I have been seeing prices drop slightly and things are taking longer to sell in the last 6-9 months as well.
With a crate motor and straight and rust free body and I'm assuming the interior is complete and presentable, I don't think $4-5K is out of the question. Spending a weekend in making it run and drive well enough to load on a trailer, $7-10K starts to look reasonable.
However, the best advice on pricing I can give is you first need to decide how long you are willing to sit on it. If you have all the time, no rush and want top dollar, price it crazy high and lower the price a bit every couple weeks until it sells. If you want it to sell fast, price it low. If you want something in between, price it in between.