Welcome utdaveling!  You've come to the right place.  The best way to determine value is by looking at SOLD listings on eBay.  There's a tab on the left-hand side of the eBay page to change from looking at for sale items to sold items. The biggest determiner is probably condition, so make sure you are comparing apples to apples as a shrink item is often double or triple what a barely used item is worth.  And a seller's reputation, as well as other factors, can also affect a sales price.  And prices have been rising over the past several years, so it's a great time to sell.  

Again, welcome!  8)

You are not the first to ask this sort of question.  Here are the titles of some relevant threads which have some good advice(use the search feature on this site):

Re: A question from a new guy...

Re: Advice?  New Seller, Long Time Collector

Re: Selling Collection - questions

info on collection

Selling books...

Okay..asking for selling advice

eBay selling advice sought - best way to get started?

You can sell stuff through Classifieds here, or on Dragonsfoot, or on Facebook, or RPG.net or lots of other places.  I personally believe eBay is the way to go.  Yeah, you can save on fees by not selling on eBay, but that's assuming the offers you'll get from the other places are just as high as eBay.  The reason you often get higher sales on eBay is that you have a larger group of buyers interested.   Acaeum buyers are often more discriminating and are not really interested in common items or those in merely very good condition.  eBay is likely best for selling off cheaper and common items.

I recommend dividing them up into smaller lots or items.  The smaller the lots, usually the greater your overall returns, but it's more work for you.

The more you are willing to be patient, the higher the prices your items will sell.  Auctions on eBay is the best way to sell things fast.  Selling with a fixed price is the best way to sell things, especially common things, for the maximum.  If you have the time, start with listing ten or so items on eBay, and see how it goes.  You will learn lessons which will change the way you sell/ship items in the future.  Start by just selling in the US before selling overseas.  Once you list some items, ask for feedback on the listings here, and you'll get more specific advice.  You might even get some offers!

There are whole threads about shipping practices, but collectors hate items damaged by postal carriers.  Books and magazine lots need to be shipped in boxes.  I use recycled boxes (Amazon boxes are usually good).  Modules can be shipped in envelopes, but they need to be wrapped in a plastic bag (grocery bag will do) and taped between two pieces of cardboard that are slightly larger than the module.  Or you can wrap the module in bubble wrap.   Again, I use recycled envelopes (bubble envelopes are best).  So, start collecting cardboard and don't throw away foam peanuts or bubble wrap. A general rule of thumb is that when you finish packing, if the contents inside move, they will incur damage in transit.  Write "Handle with Care" in marker on the outside of packages.  Media Mail is the best way to ship modules, magazine and books.  Some postal workers tell you that you can't ship magazines by Media Mail.  Ignore them.

My personal experience is that items sell better as the weather gets colder unlike right now.  I think January and February are best.

There is lots of information I left off in this post, but maybe I've given you some things to think about that will prove helpful. 8)

utdaveling wrote in Evaluation of  Shadow World / Rolemaster Lot (15 Items):Thank you for taking the time to give me your input. I appreciate the help.

My pleasure!  :)