Not sure how the average price of lithium (carbonate or hydroxide) is determined.  Past reporting of the price may help when compared to present price, but that still won't answer your question, Bodysurfer.  Hopefully someone else on this forum will chime in with a specific answer to your question.

https://www.statista.com/statistics/606350/battery-grade-lithium-carbonate-price/

"Trading Economics provides Lithium pricing based on spot prices for Lithium Carbonate, 99.5% Li2CO3 min, battery grade, traded in China." 

But Trading Economics is just one source of Lithium pricing and by basing their specification about Lithium pricing in only Chinese data it doesn't take into account the price from Australia or the Lithium Triangle.  As far as Trading Economics data goes, I still think that their graph  for lithium carbonate prices over the past 5 years is particularly revealing when comparing the current December 2023 price vs the high on 7 November 2022.  See that graph again:

https://tradingeconomics.com/commodity/lithium

Just a guess, but I suspect one of the best sources for at least EV lithium metal prices would be Benchmark Intelligence: 

BENCHMARK LITHIUM PRICE DATA

Our team of expert analysts collect market data to mineral-specific, IOSCO-compliant methodologies in order to assess prices for lithium.

Our specialist focus on the lithium ion battery supply chain and unrivalled network of industry contacts make Benchmark Minerals’ Lithium Price Assessment the world’s most trusted source of lithium price data, regularly referenced in negotiations and increasingly used in supply chain contracts.

Benchmark Minerals publishes 6 lithium carbonate (Li2CO3), 4 lithium hydroxide (LiOH) and 1 spodumene concentrate price. In addition, Benchmark derives global average prices for both lithium carbonate and lithium hydroxide as well as a lithium chemical index, weighted by volumes traded on the market.

https://www.benchmarkminerals.com/lithium-prices/?tab=table

 https://www.marketwatch.com/story/benchmark-mineral-intelligence-ev-battery-metal-prices-bb9af1b7

Wood Mackenzi is another source of lithium pricing that seems to be among the most respected.

https://www.woodmac.com/  

Fastmarkets also tracks lithium pricing:

 https://www.fastmarkets.com/newgen/battery-materials/lithium/lithium-prices/

My guess, and it is only a guess, is that Benchmark evaluation would be at the top of respected sources for lithium pricing, both for lithium carbonate and for lithium hydroxide.

That is the best I can do, Bodysurfer.  I yield the floor on your question to someone with a lot more knowledge about the subject.

Okiedo