The catalog values were quoted. However, the stamps aren't worth that much.
The first two (from left to right) are grossly off-center, and have straight edges. Value maybe two cents.
The third one looks like it may have paper toning, or its just the shade from when the image was taken. It is well centered. The stamp is worth maybe 15 cents if it is not toned. If it is toned, it will be worthless.
Keep them all on the post cards. The cards are maybe worth 25 cents each. At least you would probably find them in the 25 cents bin at a show, unless the other side has something to make it a more valuable card.
"We have one member, mostly inactive at the moment, who collects 300 on cover. "
Inactive???? Hmmm?
To expand on what Michael said...
There are two different avenues to value on these cards.
First would be the value of the usage.. the one card on the right appears to have a clean hand cancel. The one on the left is a flag cancel. There are people who collect both areas. Plus, depending on where the cancel is from, there may be some value. For instance, on US Territories there is a premium. US Territories can include areas that are currently states. I'd pay for a nice "Indian Territory" cancel. I'd pay better than $20 for a clean cancel from Guam... very scarce.
Different postmarks and auxiliary markings... Railway post offices, ship cancels, US Offices in China, different markings like covers that were forwarded, with multiple postmarks, or rubber stampings like 'train late', 'postage due' etc.
Also there are post card collectors looking for different views, different manufacturers etc. I am not that well versed in this area.
State cancels - I collect New Jersey. While the statement that these cards would be found in a 50 cent box at a show, I regularly pay $1-5 each for nice appearing covers with towns I need for my collection. Find me a town that was in existence for less than 5 years, I'd go much more.
Note that the examples I gave are rare. But there are people collecting cancels, usage and states like I do. I find the price I pay is more for the time of the seller, who has taken the time to go through the sales process for that one piece. I respect that and will pay a few dollars in that direction.
Just to add a bit to the excellent responses of others, another thing to keep an eye out for is what is referred to as Dead Post Offices. That is, postmarks from post offices that are no longer in service. These can bring a premium, depending on how long the post office was open and how many people used the post office.
The best free reference is Jim Fortes searchable listing of US post offices by state and county. Read through the instructions, as you can search by strings (partial) which is very useful if you are dealing with part of a cancel.
For scarcity ratings you need to aquire Helboccks US Post Offices volumes 1 through 8 - usually available on Ebay. They have scarcity ratings and excellent advice on how to interpret them (for example - there are many counties around the country with no active collectors - a very scarce (under 5 known) cover from those counties is only worth something if you can find a buyer.)
IPDA Chairman, Scaramento Philatelic Society #2112-vice president, ISWWSC #2966, Iran philatelic study circle, US Army Veteran, Grandfather of 6, stamp collector/seller! 13 Sep 2017 06:10:58pm