Hello, Tracy, and welcome aboard - glad you could join us.
The best way to value your lenses is to research them on eBay. See what others are selling theirs for, and price yours within that range. That's exactly what most of us here would do - the info is there for the taking.
You need to evaluate the condition of your lenses cosmetically, mechanically (aperture stopping down and opening up in a "snappy" way) and optically (look through them to see if there's any fungus, haze or dust / debris), and consider that when comparing them to what's available on eBay. Lenses with fungus or haze (or other problems) or mechanical issues usually fetch very little compared to good condition, fully-working, optically clean and clear examples.
You can also look at the user reviews in our lens reviews section. Often, people will state the price they paid. That can give you an idea of what your lenses are worth, but of course you can't see what condition the reviewed lenses were in. So for me, eBay is a better reference.
As far as advertising your lenses to sell, the Marketplace is excellent value at $10, since you can then advertise and sell your lenses with no other fees whatsoever. Plus, you're getting access to a bunch of Pentax enthusiasts who are far more likely to be interested in those lenses. Alternatively, you can sell them on eBay (in which case you lose some of the sale price on eBay fees) or perhaps in a local or national small ads paper.
Last edited by BigMackCam; 12-13-2016 at 11:11 PM.