ok, so i settled on the following formulas for a first attempt:
gather-able base value = avg gather time for one unit / resource frequency + skills cost + tools cost
craft-able base value = crafting time + parts cost + skills cost + tools cost
final value = base value * quality * demand
turns out that skills cost for gather-ables, when divided between all units gathered over your lifetime, is pretty much negligible.
looks like tool costs for both gather-ables and craft-ables will be somewhere between 1/20 and 1/100 of the tool cost.
since value of gatherables that require no tools is basically the average time required, i started by making sure the average gather times made sense. so i assigned an average gather time for all gatherables, and then set the time and chance for each appropriately. so now all gatherables do a success check every game second, minute, or hour, and the chances are adjusted accordingly.
so now i'm crunching the base values of avgtime / frequency, and i've come up with an interesting case: vines. they're only found in jungles, so the frequency is very low (0.0625. compare to 0.5 for wood, or 0.3 for stone or water, or 0.2 for reeds). reeds, tendon, and vines are only used to make cordage. but the low frequency of vines makes base value higher. so three different resources which can only be used to craft the same one item have three different values. should i say that vines and tendon are worth no more than reeds? or should i say that if you can't get reeds, you can always trade for vines or tendon, but it'll cost you more?