Collectibles : Cost or Worth
Are you looking to find out what your item is worth, as many people think that online auctions are the indicator of what an item is worth but they give a false sense of worth as they are driven by the need to acquire the item with the least amount of expenditure.

           How do you figure your collectible Cost or Worth. 
the price paid to acquire, produce, accomplish, or maintain anything:
an outlay or expenditure of money, time, labor, trouble 
having a value of, or equal in value to, as in money
good or important enough to justify 
usefulness or importance, as to the world, to a person, or for a purpose
Onilne auction tend to deflate an item say for example you are a diecast collector and you are looking for a Hotwheels Redline Club exclusive diecast.
 Item issue price is 19.95 plus they charge you 4.95 for shipping so you have a total of 24.90 that is they don't charge sales tax.
You list you item on an online auction such as ebay
The auction company charges a listing fee say it is 1.00
your item cost you 25.90 and if your item sales they charge you a final value fee and lets say it was also 1.00 now you are up to 26.90 into the item out of your pocket now say you use their payment acceptance service now they charge you a fee to accept payment and for sake of simplicity lets say it is 1.00 to accept the payment now you are into the item a grand total of 27.90

         Item                                19.95
         shipping fee                    4.95
         listing fee                         1.00
         final value fee                 1.00
         accept payment fee        1.00
 so far the total is                   27.90

Now you list your item at 19.99 and it sell at 19.99 you have just basically paid some else to take your item off your hands because you have just lost  7.91  and that is if the fees aren't any higher that the example.

So if you want to find out the estimated value of an item there are services that appraise an item.

Just to buy and speculate like the example above is not making your fortune on an online auction service, as most of the sellers don't realize that they are actually loosing not gaining. Granted there are the exception and I have seen lots of them, so do not let this example dampen your enthusiasm for making your million online

There are price guides available for lots of different types of collectibles and they are as the title suggest a guide not the set in stone value of your item.

The value of an item is always driven by demand and who is willing to pay the highest price for any given item.

So enjoy collecting and hope you do make your million.
Example 1  Diecast
Factors in figuring cost
Here are some examples when figuring the cost of an item.
                 If you are the buyer
The item itself and what it has cost you to buy it,
  Example  Book Title Gone with the Wind 19.95
  Postage paid for the item                         9.95
  Buyer fee        if a fee is charged                .95
Now that you have the item in hand do you display or store the new collectible.
  If displayed do you buy archive bags to put in the new item to keep it safe if so there is another cost. 
Are you storing the item and if so there is another cost.

As you can see that the cost of the item has increased and if you are listing items for sale is this a hobby or a business to make money and this is where you have to decide if these miscellaneous cost are enough to sell it at a profit or loss or maybe break even.

Now you take the item and you become a seller now there are a whole new set of cost to consider in selling that item.
  Now yo are the seller:
 Item Book:Gone with the Wind listed at 19.95
  Shipping is listed at                              4.99
 online sites limit the shipping fees to what is actual now  not what you want to charge
   Listing fee                                            1.00
   Final Value fee                                     1.00
   Payment acceptance fee                       1.00

Now you have sold the item now you have to buy a box, take to the post office and mail the item

   Package material  (box, peanuts, etc)      3.00
   Trip to the post office is  (fuel cost)            .50
     with the high cost of gas now this is a must 
   Time spent listing and delivering package   2hrs
    what is your time the big store figure this in to their merchandise shouldn't you if this is your business and not a hobby.

Now lets see if you broke even

Book                   19.95
Postage                 9.95
buyer fee                 .95
   subtotal is now   30.85

Now the selling part 

listing fee is              1.00
Final value fee is        1.00
Payment acceptance  2.50
Postage expense        3.50
    new subtotal is      38.85
You collected
 Item value is             19.95
postage is                   4.99

you have just went into the red (negative) on this one to the tune of 13.81
Now are you a business or a hobby
an activity or interest pursued for pleasure or relaxation and not as a main form of income or occupation
an occupation, profession, or trade in which you charge for services or goods to produce a profit
                                                                  Business vs Hobby
 Is selling online or the flea market or the local card or craft show your primary source of income or is this just one way to supplement your  income.
Is this a hobby where you do this for fun and the cost or worth of the item is not even in the factors of money gains or losses.

How you look at what it is you have to sell or trade is if you want a profit or pleasure and the two cannot meet for when they do you no longer maintain a satisfaction of the profit or the satisfaction that you just got the only Honus Wagner card (this is a rare baseball card from 1909)  available for your own collection