A value in a cell that changes automatically (using Google Finance), I want to record the lowest value in another cell.
You cannot create a permanent snapshot of a cell value with a spreadsheet formula, so you will have to use a script.
See the appendValuesToArchiveSheet script for one possible solution. You can use it to copy the value in the cell in another sheet in a log file of sorts on an hourly or daily basis and then apply
min() function to get the lowest value.