Where abouts on the strut ?
If just the spring perches, I'd use a good calcium sulphonate thickened grease (marine grease) on the threads as it resists water washout well and resists rust of the body threads.
If on the main body bushes, I have no idea what their grease may be, but I'd be looking at probably a calcium sulphonate complex grease with 3-5% moly, something like one of CAT's heavy machinery greases, particularly their 'Desert Gold' grease which uses a synthetic base oil and is formulated for high temps/high loads. (there can be very high bending loads on an inverted strut body and I'm guessing the damper body runs in a DU bush inside the lower strut ?? )
$90 is a lot of moolah for a small amount of grease