Tubeless Valve for Inserts (single) - Presta - Alloy - 46mm
$50 for a pair CushCore compatible valves seems a bit steep... Doesn't it? Here's some insert compatible tubeless valves that do exactly the same job whilst leaving you enough cash to shout beers for yourself and a mate.
These valves seal well to the rim and, since it's a presta valve, it has a removable core so that you can clean it when its inevitably become blocked by overambitious tyre sealant. At 46mm long it fits even reasonably deep carbon mtb rims. T-shaped air passages allow air to flow unimpeded by insert and a hex slot at the base also allows you to hold the valve still, just in case you ever need to (valves can get rather slippery).
Note: This is one valve, if you want to purchase a pair you will need to purchase two...