For low quantities of PCBs, there are two main services available that I am aware of: OSH Park and iTead Studio. They have their pros and cons, but a new kid has come onto the block: circuits.io. They use OSH Park’s facility, but have a different pricing formula. I have done some analysis to find the best vendor for the project.

This is how the prices are described on the websites. (circuits.io I had to calculate) These are important because these are the prices you pay upfront. You can call this the “prototype cost” since a lot of the time you might not even want the extra boards.

OSH Park: $5.00 / square inch for multiples of three
Circuits.io: $0.87 / square inch for multiples of three + $6.50 flat rate
iTead Studio: Tiered pricing starting at $10 for any size up to 3.875 sq in for multiples of ten
Upverter: $19 + total sq in

Upfront Cost

If you take into account the extra boards you receive, then you get the actual cost per board. This is what you should be looking at for a production run, although you might want to consider a different firm altogether if you are making more than a few boards.

OSH Park: $1.75 / sq in
Circuits.io: $0.29 / sq in + $6.50 flat rate
iTead Studio: $1 for any size up to 3.875 sq in
Upverter: $19 + total sq in

Actual Cost per board

This graph is essentially the same, but it takes in to account all the extra boards you receive. For example, the point (4.76 sq in, $7.67) actually represents (three boards of 1.58 sq in each).

Notice in this graph that all the curves are scaled except for Upverter, which did not move at all. OSH Park and Circuits.io intersect in the same price, but with three times the area. Also notice that iTead Studio beats everyone price-wise at almost all sizes.

Special notes:

• The boards from OSH Park/Circuits.io are of higher quality than iTead Studio. How much that matters depends on how fine the traces need to be. They also come in an ENIG (gold) finish instead of the default HASL (solder) finish. If you want the ENIG from iTead, its a $20 upgrade.

• Circuits ordered through Circuits.io must be made ON the circuits.io website. Their layout editor is in infancy, but their price is good.
• Circuits.io does not appear to allow ordering quantities above 12 boards on their pull-down menu. This might change if you email them, but if the limit is really 12, then their “cost/board” curve ends at 12 × (area in sq in)

• Designs to iTead Studio must fit within a square containing the maximum area of that tier. For example, the first tier is 5cm × 5cm, so the board cannot have a dimension longer than 5cm.
• This analysis does not include panelizing. Panelizing is allowed on iTead Studio, but they do not allow more than 5 sub-boards on one design, so it is limited. In addition, boards must be cut yourself. (unless you make small bridges that snap off) If you do panelize though, the effective cost per board is divided by the number of panels on each board.
• This is for green PCBs from iTead Studio. Color costs more.
• I did not consider shipping for iTead Studio because it varies by country. The others have free shipping to the US.

• The actual Upverter formula is $19 + (slider multiplier  ×  total sq in  ×  (num_layers-1)), explained here: http://support.upverter.com/customer/portal/articles/821190-how-the-cost-time-slider-works Frankly, a “~2 month lead time low quality” PCB does not sound usable. That is their minimum slider value.
• Upverter offers an BOM ordering and assembly service along with its PCBs, but only the PCB prices are considered here.

Conclusion:

• Order boards from iTead for maximum possible savings unless your board is < 0.59 sq in, in which case order from OSH Park.
• Upverter boards are very expensive depending on what “slider value” you choose. Increasing the slider value will increase the slope of the graph.
• Order boards from Circuits.io if you can tolerate their basic circuit editor and your design is larger than 1.57 sq in

Matlab code used to generate graphs:
http://pastebin.com/nxuUtRG8 http://pastebin.com/n06Z67PP