While these aren't RGB pixels, the process is the same for any panelized design I create, including the layout for the WS2801 + SMD RGB pixel in this thread. I needed to make 630 bright green LED pixels and rather than buying the LilyPad pieces (https://www.sparkfun.com/products/10046) which would've cost me upwards of $500, I decided to make my own. On a 50mmx50mm piece I can cram 23 of them: a grid of 7x3 plus two extra to fill the rest of the board.
Production of boards was $30 + $5 shipping. LEDs and resistors just over $200. My time: priceless. 
Here's me cutting a single board into pieces, takes me a little over 2 minutes each (I already trimmed off the extra two that are along the top edge of each board). I should point out that these are 0.8mm FR4 boards, however the WS2801 pixels I created above were done on 2mm FR4 boards. Cutting is just a bit slower for those.