For 6 euro's I built a counter which measures frequencies from 1 Hz till 50 MHz.
I ordered the "Do It Yourself" kit here:
The counter can also be used as crystal tester.
The counter is designed around a PIC 16F628 that also contains a table with most used IF frequencies which you can add or substract from the measured frequency.
Very nice design with big LED displays !
The counter works ! 16 MHz X-tal here under test
Close look with 4 MHz X-tal under test