One of the better ways to determine their value is to look at what similar minis sold for on eBay. Log in to your eBay account (or create one). Type in descriptor words in the search bar (25mm, Grenadier, miniature, etc....) click search to see what items are selling for and
then click the "sold" box on the left-hand side of the page to see what they actually sold for. The sold for items are way more accurate in giving you an idea of what your items will sell for. Minis in blisters sell for more than minis out of blisters. Items from reputable sellers go for more. Don't forget to factor in shipping in your evaluation. I have a large vintage collection of minis. If you have a specific question, feel free to ask. If you want offers from people on these forums, just post some pictures.

Truth is worth finding and life is too short to work for money.