Conditional Autosum

[GMOODY]

Good afternoon everyone
I've got a spreadsheet that has 3 columns in it that I need to put a conditional autosum. Basically, what I want to be able to do is say that if a cell is empty, put in the autosum function since there could be anywhere between 1 and 50 lines above to be summed together. There are also some lines in the data (that I can't remove) that don't have a quantity in them, so the only way I can think of is a conditional formatting.

Any help is greatly appreciated. I've attached a sample file. the dark coloured lines are added by a macro that I need to add onto. I want to say that any cell above the word "SKIDS" need to have the autosum function, or any cell directly below a number, or something along those lines.