Dave,
This website will tell you all you need to know.
http://mgshooters.com/index.php
The .50 BMG M2HB ground mount rental is $4 per round (see under 'Rentals'), which I gather is a flat rate to shoot the weapon, so a standard liner would cost you $400 - and take less than a minute to send down range!
Next shoot is 22 to 24 March 2019.
Mike