Nested Max Statements

[#1]

I am trying to get a unit price for a particular PO# based on a selected date. I need to get the current unit price and compare it to the last unit price recorded, which could be different dates for each PO#. This last part is the one I am having problems with.

I am not having a problem grabbing the last date that the PO# has a unit price. I am using the following formula to find that date:

=Max({<PODate = {'>=$(=addmonths(PODate,-12)) <=$(=max(PODate))'} >} PODate,2)

This works great and tells me the last instance of the date based on my current date selection for each PO#. Now I just need to grab the unit price at those dates. For instance, below if I select 8/1/09, I want to grab the unti price for 7/1/09 for PO# 1 of 15.50, and the unit price of 7/2/09 for PO# 2 of 10.50, etc.

PO#	Site	Date	Unit Price
1	south	8/1/2009	20.50
1	east	7/1/2009	15.50
1	west	6/1/2009	10.50
2	south	8/1/2009	9.00
2	west	7/2/2009	10.50
2	west	6/1/2009	10.50
3	west	8/1/2009	9.00
3	west	6/1/2009	25.00
4	north	7/3/2009	30.00
4	east	6/1/2009	18.00

I can get it to provide the dates using the max function above, but when I try to get the unit price, I am having trouble. My thought was to nest the first formula into another set analysis (in bold below) where I would set the PODate equal to the date evaluated from above. When I use the below, the nested max statement only gives me one date and not the individual dates from the original formula.

=Max( {< PODate = {'=$(=Max({<PODate = {">=$(=addmonths(PODate,-12)) <=$(=max(PODate))"} >} PODate,2))'}>} unit_price)

Not sure if that has to do with the double quotes I used?? It won't evaluate anything if I use anything other than the double quotes for the nested set analysis.

Maybe I am looking at this the wrong way or using the wrong function for the second part?