As others have mentioned, it really depends upon the individual stamps and condition to determine the "saleable" value. ALL common stamps listed in the catalog may have a minimum value of 25c, but that is not anywhere near what you could expect to get for them. The 25c is a reference value for which you may expect to pay a dealer for that single stamp, since they have taken the time to identify and organize it for you to select for purchase.
In a collection or assortment, even if the stamps are all different, the minimum value stamps may sell for 1c or 0.1c each (or less) on average for the grouping. Most sellers on
ebay and other venues may typically see 5% to 10% prices for some better catalog value stamps than the minimum value ones.
Dealers need to buy at a much lower percentage of catalog to be able to move material at 20-25% catalog (if that), and that is for sound condition material.
So, valuation (to sell) really depends upon what you have.
A description of how you are valuing them (for example, do you count any stamps with catalog value less than $1?) and condition would be helpful.
Pics are great to show so we can opine more usefully!