Yes, that is a good price, but AFAIK all the US prices are quoted without taxes, to make them seem smaller, unlike in most other countries, so with taxes included I assume that the real price is about $400/kWh, which matches the price that I have found meanwhile for a similar battery in UK.
Therefore, the current price for Na-ion batteries is only 3 times less than LFP (the endurance and lifetime are claimed to be about the same for Na-ion and LFP).
Still, this price ratio of 3 remains a significant difference and it is very likely that in the future the price of Na-ion will decrease at a much higher rate than the cost of the mature lithium-based batteries, when more manufacturers will begin to make Na-ion batteries.
https://www.currentconnected.com/product/sk48v100/
You can easily find other brands for less than $300/kWh, and plenty of review/teardowns on youtube.
Edit: adding "Typical capacity at 80% DOD @.5C Rate is over 7000 Cycles" so if you bring your battery to 7000 80% cycles at 0.5C you got 28000 kWh out of it, so 0.059 USD/kWh out of the battery (and you still have 4 kWh usable in the battery so many more cycles).