Okay...I'm interested in it now I'd like you to help me where to start from.
Provide me a link to good website where i could know about this.

I have started learning Xilinx ISE and verilog...

By the way...designing of decoder was pleasure making. Now, I'd go with binary to BCD decoder and then (two) BCD to 7 seg decoders...AND I'M DONE

 

Well, I haven't used CPLDs myself, but I have used Xilinx ISE and their FPGAs with Verilog. That is tremendous overkill, but this is certainly a good learning project as an introduction to Verilog and FPGA programming.

Really the cheapest way to do it is probably a cheap microcontroller (about $1.00 or less). Something like an AVR is an easy way to go. If you get an AVR development board like any Arduino-compatible board, you will be working with a platform on which you can take that little AVR microcontroller and drop it (or any of its variants like the ATtiny series) into your own PCB with few extra components.

You could look at Adafruit's Barebones AVR board, or the Really Bare Bones Board (RBBB) if you want something minimal and be “close to the metal”. That will help you really learn the AVR in depth. You can use the Arduino IDE and language/libraries with many AVR boards like the RBBB, and that is really slick, but you might want to start down at bare metal if you are so inclined. (Bare metal in this case means avr-gcc + avr-libc + your program main() function etc. That is in contrast to Arduino which provides lots of higher-level stuff making things both easier but putting more between you and the basic MCU stuff.)

Adafruit has some good tutorials on programming the AVR. Also, AVR Freaks is a great resource where you will find lots of help if you need it.