So after reading this I am not sure if RadAlt will be good for your white out conditions over glaciers.
True RADALT can missread somewhat but in my experience flying many different helicopter types with RADALT the error is no more than 50-70 feet over loose snow or in some glacier conditions. Most of the time it is very accurate but one has to be aware of the errors and use secondary means of confirming altitude over ice at very low altitudes.
$12K is worth it expecially in the GX where you can use the integrated panel to give you voice altitude warnings. It also works with the barometric altimeter but much more accurate with the radio altimeter.