Just had a fun conversation with an administrative assistant in one of our colleges. She needs to order a flier or a postcard or a brochure -- she's not sure which. They may want between 200 and 500 but maybe less -- they're not really sure of the quantity. They may want to mail these, or maybe just hand them out. Can I give her a price for how much this will cost?

1) I need to know what exactly I'm designing, printing, and mailing -- a brochure, flier or postcard? What size? Does it fold? Printed on both sides or just 1? Full color or black and white? What kind of paper? If it's a postcard, it needs to meet minimum postal requirements for thickness.
2) I need a quantity to figure the price. Actually I need a size and quantity to determine if it's more economical to print these digital or litho -- the price will vary widely.
3) Postage -- will this be first class or do you want to use the our nonprofit indicia (minimum 300 quantity)? If this is a postcard it needs to be no larger than 4.25" x 6" to qualify for postcard rate. If it's a brochure, it'll need to be tabbed closed or inserted into an envelope. If it's a flier, it can mail flat or be folded and tabbed.
"Oh, just give mea price for every possible option, then I'll decide."
It's obviously not possible to give her an exact quote for every possible permutation, but I would expect a business to be able to give me a general range: "Brochures run from $A to $B apiece, depending on how many you have and what options you want. Flyers tend to be around $C per batch of 100. Postcards are $D-$E pre-stamped and ready to mail or $F-$G if you want to process them yourself. These are all really general numbers, mind you, but they should help you figure out what fits into your budget."
I'm reminded of when DH and I wanted to buy a sofa - one or two places in town refused to even give me a general price range for their furniture. I know sofas can range from a few hundred up through several thousand dollars - I just wanted to know whether their store had $$$ or $$$$ options! The places that told me "Just come in and customize something and see for yourself!" - yeah, no. I ended up doing that with one place, only to find I had wasted my and the salesperson's time because even their cheapest options were way more than I wanted to pay.
That may work at a quick print shop that runs out photocopies on a letter or tabloid-size sheet of paper on a Xerox -- like FedEx Office. But I'm a professional graphic designer and not a print shop. I don't do the printing myself. I bid it out to various vendors based on what the project is, and go with the best bid. The prices vary widely not just based on whether it's a postcard or flier, but on the vendor, quantity, size, color, mailed/not mailed etc. The majority of the projects that I work on are going to print on an offset lithography press.***
If she called and asked how much 500, 4.25" x 6", full-color postcards, mailed might cost, I could pull up a similar job that I've done recently and give her a really good idea, but in essence -- to use your example of furniture shopping -- she did the equivalent of calling an
interior designers office and saying she doesn't know if she wants a new sofa...or 2 bedroom night stands, or a dinning table with between 2 and 10 chairs and she's not sure how big for any of these because she hasn't even decided on where this mystery piece of furniture will go...can they tell her how much that will cost. THAT what? There are literally too many variables to even begin to give a reasonable estimate.
***If you're interested in a more detailed description of printing technology: offset lithography uses metal printing plates usually aluminum to put ink on paper. This produces a higher quality, better color, and sharper image. Ink soaks into paper so there is no chance of it "rubbing" off when going through mail processing equipment. You can use spot colors like Pantone, or varnishes that create a really high gloss finish. The largest sheet size is usually 26" x 40" which allows for multiple jobs to print at one time.
Digital printing is like an office Xerox on steroids: powered toner is adhered onto the surface of paper using heat. The pros are that it can do small jobs quickly and cost effectively. The cons are that it has a higher per sheet cost than offset depending on the quantity, the quality is (in my opinion) not nearly as good especially if the finished product is going through the mail as toner can flake or rub off, they aren't as color accurate especially if you want to match a Pantone color, the only varnish available that I've seen isn't very good at all (I just tried it on an invitation project and nobody could even tell it was supposed to be extra glossy) and generally the largest sheet size is about 14" x 19".
This is a pretty good summary of the differences:
http://www.pinscreative.com/articles/digital_vs_offset.htm