The offer of 10 cents a cover for these types of First Day Covers (no cachets, addressed, missing the high face value stamps) is not unrealistic. You can buy this sort of thing wholesale for something in that range. There are still some active First Day Cover collectors and for certain FDS with certain rare cachets in perfect condition and without addresses they pay several dollars to more for them, but the lot you describe would not be one of them. Modern FDCs (1930s to the present) is a situation where supply dramatically exceeds demand for most all but the rare ones and so now is a good time to be having the fun of buying and building a collection while selling one can be disappointing. My suggestion is to group your FDCs that you want to sell in logical groups such as the one you describe and put them up on eBay
with staring bids of $1 and see what they bring. Collectors there will bid up whatever you are selling to within a good ballpark of the current commercial value. If you have older FDCs from the 1800s through to the 1920s or so you would likely get good prices and not so much concern about cachets and being addressed so long as the cancel is very clear.