You can read about the Tzolkin Mayan calendar on Wikipedia http://en.wikipedia.org/wiki/Tzolk%27in. It is one of several calendars, and consists of 13 numbers and 20 day signs which appear in 260 combinations that rotate. In other words, with every change of the day the numer increases from 1 to 13 and then back to 1 again. Similarly the 20 day signs rotate.
What I needed was a frame and face with the numbers and day signs on it, which I modeled on the Sleek World Clock, and relied on scottbez1's great instructions on printing the face and making the actual calendar. The electronics are Arduino and I put the code together from bits and pieces to take the date from an RTC, calculate the Julian Date and then work out where in the two Tzolkin rotation that day falls. LED's are controlled via a shift register.
This is my first ever Arduino project - a testament to the great ease of use of this amazing technology!
Step 1: Assembling the Electronics on the breadboard for testing
18 white, 5 red, 5 blue, 5 yellow LEDs (www.sparkfun.com SuperBright $0.50 each when bought in packs of 100) - $17
33 Resistors 330 Ohm 1/6th Watt - $2
1 Arduino Uno - R3 board www.sparkfun.com - $30
1 Real Time Clock Module DS1307 BOB-00099 www.sparkfun.com - $15
5 Shift Register 8-Bit - 74HC595 www.sparkfun.com - $7
1 Wall Adapter Power Supply - 9VDC 650mA www.sparkfun.com - $6
2 printed transparencies (see attached pdf on Step 2) - $1
Total cost: $88
Also: prototyping breadboards, prototyping leads, wire etc
Cardboard and other household items
Total cost: around $44 (using standalone ATMega168) or $67 (if you buy a full Arduino)