Sagedawg,
As far as "prep" that's up to you... you can skin stretch and dry your pelts, skin and freeze, or sell "in the round" (the whole animal).
Often times, the whole animal has a value that exceeds that of the pelt, and can save you the effort of skinning and handling.
There's a video out, by a gentleman named Blaine Eddy, on skinning coyotes, that would give you a good leg up on things, if'n you decide to put up your own hides.
And, I sell some really nice adjustable 'cat/coyote hide stretchers, made from cedar (and many other sizes too).
As far as a Spokane buyer, I'm not real sure on that, but the best fur buyer around, Geo. Brady of Cascade Biological Supply, is up north in Pateros.
Many taxidermists are interested, so that may be your best "local" option.
The Washington State Trappers Assoc. has a fur sale each spring, one on each side of the hill.
Otherwise, to save fuel costs, a chest freezer will store enough coyotes to make a trip to a fur buyer worthwhile.
Summer coyotes are WORTHLESS, if you're going to sell fur, you'd better wait 'til it primes up (in Nov).
If I can be of any more help, with this, let me know?
Krusty