Simplifying cost calculation using array instead of IF statement

Unless I'm mistaken, after spending a bit of time looking at your formulae, I think you could take good advantage of INDEX and MATCH to zero in on the relevant cells in this table

These hyperlinks will point you to a good reference site to learn how INDEX and MATCH work. And again, unless I'm mistaken, you would be able to eliminate the many IFS conditions comparing J4 with the top row to directly zero in on the appropriate column, and then again to identify the appropriate row based on the items down the left of  this table.

Given how well you've mastered IFS and XLOOKUP in combination I have no doubt that you'll be able to use INDEX and MATCH equally well.

One other recommendation, assuming you are working in Excel rather than Google Sheets, you could use (on a Mac) a combination of the Option key and "Return" to format your extensive formulas as I've done with the formula in Q12, below; they're much more readable this way.