many measurements are done with scopes
but if you need lots of digits, for sure you need counters, tcxo ocxo based time base
and yes they are getting hard to find, even the used ones goes for high $$$ as you wrote
Racal Dana used ones come a lot
Agilent / Hp ones too, and some added option board are available ...
one who get some attention PENDULUM CNT-90 and its fluke counter part have some added board option to crank their frequency ranges ...
With a good design, you can do them with Avr's or Pic mcu's
and some chineesium projects sold on Fleabay, Ali etc ....