This has been a trend with some of the truly scarce Lie-Nielsen tools over
the past couple of years. There's always been high demand for their tools
on the secondary market. I think some folks came to realize how scarce some
of their tools are. High demand and low supply equates to high prices. The
left-handed edge plane you mention is one of those rare ones. The no. 9
mitre plane is another. There won't be any more of them made.

The pandemic caused L-N to cut back on their production while demand for
their tools was skyrocketing. This caused a short term increase in the
prices for some of their tools that are still being made but hard to find.
I have a shoot plane here that I waited too long to sell.. They were going
for $1k +regularly on eBay. Now that they are back in production the prices
are back to normal. Ah well.

Josh