Summarise list and show total depending on 3rd cell

Hi, hope someone can help me with this problem?

I have a excel sheet which contains 3 columns. Column A lists the cost, column B lists the quote reference and column C lists the purchase order number (once it has been given).
See attached image rows 2 to 11

Screen Shot 2018-02-14 at 14.55.58.png

I want to create a summary at the end of a table which will show the total value for each quote reference where the purchase order number hasn't been supplied.

The data changes on a regular basis so I can't use fixed names / ranges etc, only a fixed start cell and end cell.

Try this
Enter array formula in B15 and copy down
***Array formula
...confirmed by pressing CTRL+SHIFT+ENTER to activate the array, not just ENTER.
You will know the array is active when you see curly braces { } appear around your formula.
If you do not CTRL+SHIFT+ENTER you will get an error or a clearly incorrect answer.

Formula:

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then Enter SUMIF formula in A15 and copy down

Formula:

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Assuming that you are asking about having the array in A15:B17 update when a PO number is placed in one of the rows for a particular Quote Ref, as in if ME-17-750 is placed in cell C4, then use the following formula for cell A15 and down:

Formula:

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If there were PO's in both C4 and C5 the HouseB_Jan would not be displayed in B15 leaving cell A17 displaying a dash. You could hide that using a conditional formatting rule the sets the font of cells with a value of zero to white applied to the range A15:A17.
Let us know if you have any questions.

You're Welcome. Thank You for the feedback and for marking the thread as 'Solved'. I hope that you have a blessed day.