I found a nice auto ranging frequency counter online here:
Did not have those 7 segment displays, considered an LCD interface, but why not use RS232, and power it from the RS232 too? Just a probe you can bring along with your laptop, saves weight :-) So.. modified that code a bit:-)
This is what the output looks like: ftp://panteltje.com/pub/RS232_frequency_counter_output_on_monitor_img_1515.jpg
When it is measuring it's own crystal (20MHz): ftp://panteltje.com/pub/RS232_frequency_counter_img_1513.jpg
This is how simple it is, only 7 components, not counting some input FET: ftp://panteltje.com/pub/RS232_frequency_counter_diagram_img_1516.jpg
This is the modified asm source for a PIC 16F648A: ftp://panteltje.com/pub/counter-0.1.asm Could not get it in a 628, wanted to leave the original 7 segment code in too. Will have a go later perhaps to see if I can eliminate those few bytes over 2 k.
Resolution is 1 kHz on the MHz range, and 1 Hz on the kHz range. The crystal will need a trimmer to set it to exact frequency, used 2 x 22 pF here.
Oh, yes, that is a PIC. Total cost, without input FET... maybe 10 $? This could fit in a D connector shell, and have a pin stick out of it to measure with.