While I strongly suggest multiple sources of research, to *really* dig into things, check out "Opal Identification & Value" by Paul B. Downing.
Even still, opals are a rough item to price due to their nature.
Every single opal is unique. What you hold in your hand is one of a kind in the universe. None before, nor after, will ever have that fire pattern, or that cut, etc.
Because of this, things can get very subjective. Where one person might pass it over, another person would be willing to pay well.
One opal I can think of in particular was sold many years back, when I was just starting out. It was a black opal that had almost no flash, until you looked at it in the sunlight. Then, out of the darkness, at certain angles, it would light up with amazing fire. Very acute angle visibility with opal fire is not very desirable in many cases, but, if I had the money, I'd pay quite a bit to have that opal. Because it means something *to me*.
To start out, however, as you mentioned that some are crazed, get someone with a good eye, a loupe, and a soft white light source to "candle" every last one of them. Sort out the ones that are crazed, figure out which of them have cracks, and set aside all the ones that are in good condition.
Crazed and cracked opals are rarely worth anything. Some cracked opals, if large enough, can be re-cut into smaller stones that will have value, but you have to question why they cracked in the first place.
Once you have all the "good" opals set aside, sort them by general color. Black, white, and crystal (clear). Obviously there are many variants of each, so just do a quick sort of the obvious ones for start.
Next, simulate sunlight (or use actual sunlight), and look them over for their fire. Again, sort them out, but this time base it on how "bright" they are. Again, this is somewhat subjective, but if you have a bunch of them, some will be clearly brighter than others.
Lastly, weigh them and keep track of their weight. and if it's not too much trouble, measure them for their size.
At this point, you're going to be ready to make some decisions on price. You have a few options.
One: obtain the book I listed above and spend a week studying it, then research other sources on the internet to confirm for yourself if you trust what Mr. Downing has to say. Once you are more knowledgeable about opal, you'll be ready to make some guesses.
Two: Gather up the best and the brightest of the opals, and take them to a GIA certified appraiser and let them give you a value. However, the cost of the appraisal could easily outweigh the value on the opals.
Three: Take a couple pictures (different angles) of the opals, and post them here and let us lesser qualified people take a stab at pricing them.
Out of these three methods, option 2 is the best option for nailing down a price, and a good appraiser will probably offer documentation that can be used for insurance purposes.
All of this, of course, depends on how much time you have to deal with the opals. If it is not something you are willing to invest some time into, you won't be able to get the value out of them, and while it is unlikely, you might lose out on a real gem.
Rough opal, like cut opal, has varying levels of quality too, but nailing down a value isn't as easy because they have so much potch in the way at times.
If all else fails, just send everything to me, and I'll hoard them like I do the rest of my opals. :D