Generally frequencies that high are done using prescalers. It's also
possible to do it with a mixer, and there are some other specialized
techniques. Several companies make prescalers. They tend to be
expensive and not very easy to find. An alternative way to do the
prescaling is to use a PLL chip. Many of them (like the National
PLLatinum series and the Analog Devices parts) have one output pin that
can be programmed to monitor the divide-by-n chain output, and you can
program the divide-by-n to give you some useful fairly large division,
to get down to a frequency that's easy to count at that output pin.
The PLL chips like that tend to be inexpensive and more readily
available than the prescalers. So what if you're not using about 75%
of what's in the chip? You may want to use an MMIC gain block between
the signal input and the PLL or other prescaler to get the sensitivity
up a bit.

Cheers,
Tom