I use ExpressPCB. They provide free, limited design software that allows the user to create a schematic and layout a board. The final result is a proprietary file only they can use to produce a board. The user can get an estimate of board cost by clicking a menu selection. Here's a link to the page where you can start investigating costs:
**broken link removed**
From here you can jump to other pages, even download the free design software.
I took advantage of their Miniboard Pro service. This means the board's dimensions must be 3.8" by 2.5". This service lets you get three boards for $91. This is $75 for the boards ($25 per board), about $10 for 2-day shipping, and the rest is tax. This gets you a professional board: drilled, solder mask, silkscreen (one side only), plated-through pads and vias, FR4 board material.
They offer a Miniboard service where the three boards are just $51 ($17 per board), but no professional finishes, just exposed traces.
Most board houses quote by cost per square inch. The three boards above are 3.8 by 2.5, so 9.5 square inches. Divide the $25 fab charge per board by the square inches, you have about $2.63 per square inch. This is typical. I have checked out other board houses and they seem to come in around this range. Sparkfun.com has a PCB fab offering: $2.50 per square inch. The difference is, you may wait up to three weeks to see your handiwork, versus a fab house's typical two to seven days or so. Then again, some fab houses quote a really low square inch price, but sock it to you with a huge set up charge. After you factor that in, you end up around 2.50 per sq. inch again.
Of course, the number of boards in your order has a big effect on the final price. The 2.50 per sq. inch mentioned here is probably typical for prototype quantities.
Cost is not the last concern. Some of my gripes with ExpressPCB is they don't do double-sided silkscreen, or do internal slot cutting, or pre-scribe panels so you can break boards off by hand later, among other concerns.
Every fab house has design criteria the board designer has to keep track of. They tend to specify trace width and clearance minimums, minimum drill size, a list of available drill sizes, limitations as to how close to get traces and other copper to the board's edge (due to router inaccuracies), and a host of other factors.
As a for-instance, ExpressPCB will go down to a hole size of 13 mils (13 thousandths). This makes for nice, small vias. For $60, these guys will take your submitted design and convert it to industry standard files you can submit to most any other fab house for quotes and manufacture. But I found several of these fab places won't do holes as small as 13 mils! They tend to use the next size up. Which, if they get sloppy in their drill placement, could kill your via(s). This suggests you find a select few fab places with manufacturing specs and shipping times you can live with, then do your designs specifically with them in mind.
I have just started designing boards and having them made professionally, so take all this with a grain of salt.
Have a nice project.
kenjj