An unaddressed FDC with a common cachet of Scott #C46, the 80c Hawaii stamp, issued on March 26, 1952 has a catalog value of $20.00. This is for a cover in very fine condition without tears, stains, or smeared postmarks, and with a sound, well-centered stamp. A neatly addressed, cacheted cover would be discounted; I estimate to about 50% of the listed catalog value. A cover with a scarce cachet (not ArtCraft or Artmaster) may command a small premium. An addressed cover without a cachet would have a catalog value of about 1-2X the value of a used single of #C46, $1.25.
Unaddressed FDCs without cachets are rarely seen. Most FDCs without cachets were prepared by collectors before the so-called "grace" period came about. The plain envelopes were sent to the post office with instructions to the Postmaster to affix the stamps, apply the first day cancel and send the cover back through the mail. Unaddressed covers were sent in bulk by dealers to the issuing post office and returned in bulk to them, so they needed no address. These covers were nearly always cacheted.
However very clean unaddressed FDCs without cachets can potentially be used by artists to add a cachet and sell at a profit. So the right person might be willing to pay a little more in this case.
Thanks, t360. That's exactly what they are, covers returned in bulk, as you describe them. Have a box of the 4-cent Project Mercury FDC, Scott 1193 from 1962, that my father had sent for. They don't have cachets. Know practically nothing about FDC's since I never had any interest in them. It looked as if you said an addressed cover without a cachet could be worth 1 to 2 times a cover with a cachet. Was just wondering how one without both an address and cachet might fit into the mix.