Here below is a data table:

We want to calculate the price value in column B according to the quantity in column A, and the calculation should follow the rule: different quantity intervals correspond to different prices, as shown in the table below:

Enter in cell B2:

=spl("=[15,13.75,13,12.5]([30,50,100,300,500].pseg@r(?1))",A2)

Then drag B2 down to every relevant row:

The idea of the calculation is to use the pseg function to calculate which interval the quantity value belongs to [30, 50, 100, 300, 500], and then take out the price of the corresponding interval from the price sequence [15, 13.75, 13, 12.5] and return.

esProc Desktop and Excel Processing
12.4 Reference multi-column data from association table
12.6 Use association table to handle interval association