I placed an order for the transponders this past weekend from JLC. The total for 5 boards came out to a bit over $210 USD ($60 in tariff+$50 in shipping) with a $10 new user coupon for five panels on github. It appears production won't be effected by the February holidays and they'll be finished and shipped out by the end of the week.

I did get a warning the 20mhz crystal used on the board was in low supply, preventing me from ordering 10 boards. The suggested alternatives use a different footprint, HC-49S-SMD. If you broaden the search there are SMD3225-4P alternatives but the capacitance is different from the 15pf in the bom.