All of the information given thus far is correct. 51 cents (50 cents + 1 penny to press) is the cost. For pressed quarters, it's $1.25 ($1.00 in quarters + 1 quarter to press). And there's 1 pressed dime machine in the arcade in Tomorrowland (I don't recall the price, though).
We've pressed a penny here and there over the years, but on our upcoming trip we're planning to get a TON of pressed pennies. A bit of pre-trip preparation advice for pressed penny collectors:
* Use pre-1982 pennies. After 1982, pennies are mostly zinc with a copper coating and when you press them the zinc coloring comes through. Prior to 1982, pennies are mostly copper with very little zinc. In case you're having trouble remembering the year, it's simple: 1982 was the year Epcot opened...get pre-Epcot pennies.
* Shine those pennies up before you press them. We put 1/4 cup of vinegar in an old pickle jar, added a teaspoon or so of salt, and then dropped in a dozen or so pennies at a time. Swirl them around and after they start looking new-ish (10-30 seconds), remove and rinse them off. While they're still wet, rub some baking soda over them by hand and they usually shine up quite nice.
* Go buy a few of those M&M tubes at the store. Empty the M&Ms out and use them to carry your quarters and pennies. I've found that of the larger M&M tubes holds $20 in quarters (enough to press 40 pennies).
* Get one (or two or three) of those pressed coin books. You can buy them at WDW or on Amazon. Once the pennies are pressed, you won't want to carry them around with the unpressed pennies, so it's good to have those books handy.
* Go to
http://www.presscoins.com/ and get to know where different machines are located and what designs are available. By my count, there are currently over 500 different designs in and around WDW. That'd cost you over $250 (not to mention a lot of time) to get them all, so it's best to narrow your choices and have a plan around which coins you want to get.
Have fun! I know we're looking forward to flattening a few coins in a few weeks.