Using Lookup and Reference functions with named ranges

Note: Edited to add row & column references to make table easier to read
         Edited to remove ambiguity about manual calculations

Hello Experts,

I'm trying to use Lookup and Reference functions to dynamically define the ranges used by various statistical calculations like AVERAGE, STDEV, CORREL.

The approach i have in mind is to use a a user defined functions for each calculation, using SecurityA, SecurityB, #daysHistory as required parameters.

My workbook has two sheets:

PairList! (note: this sheet might have up to 700 rows)

user input---------------------------------   Calculated values-------------------------------------
SecurityA     SecurityB    #DaysHistory    fnRatioAvg      fnRatioStdDev             fnCorrelation
1 HK            20 HK              5                HELP!           i'll do myself later      i'll do myself later
4 HK            20 HK              5                HELP!            i'll do myself later     i'll do myself later
...
...


Price! (note: this sheet might have up to 65000 rows and 700 securities)
I have currently sorted it ASCENDING, but could change to DESCENDING if the lookups are more efficient.
      A                      B       C
1      SecurityID                      Date      Price
2      1 HK Equity      8/10/2006      84.85
3      1 HK Equity      8/11/2006      84.9
4      1 HK Equity      8/14/2006      85.25
5      1 HK Equity      8/15/2006      85.6
6      1 HK Equity      8/16/2006      86.85
7      1 HK Equity      8/17/2006      87.85
8      1 HK Equity      8/18/2006      88.25
9      1 HK Equity      8/21/2006      87.05
10       20 HK Equity       8/10/2006      13.48
11       20 HK Equity       8/11/2006      13.62
12       20 HK Equity       8/14/2006      13.52
13       20 HK Equity       8/15/2006      13.5
14       20 HK Equity       8/16/2006      13.74
15       20 HK Equity       8/17/2006      13.62
16       20 HK Equity       8/18/2006      13.6
17       20 HK Equity       8/21/2006      13.5
18      4 HK Equity      8/10/2006      28.8
19      4 HK Equity      8/11/2006      28.7
20      4 HK Equity      8/14/2006      28.55
21      4 HK Equity      8/15/2006      28.5
22      4 HK Equity      8/16/2006      28.8
23      4 HK Equity      8/17/2006      28.8
24      4 HK Equity      8/18/2006      28.65
25      4 HK Equity      8/21/2006      28.35
...
...
Assuming data for both Prices! and PairList start in cell A1 (with headers), manually the calculations for the first pair (1 HK / 20 HK) would be
={AVERAGE(Prices!C7:C9/Prices!C15:C17)}
={STDEV(Prices!C7:C9/Prices!C15:C17)}
={CORREL(LN(Prices!C7:C9/Prices!C6:C8),LN(Prices!C15:C17/Prices!C14:C16))}

The result table looks like this:
SecurityA                      SecurityB            #DaysHistory      fnRatioAverage      fnRatioStdDev      fnCorrelation
1 HK Equity      20 HK Equity      3      6.4624                      0.0230                       7%
4 HK Equity      20 HK Equity      3      2.1071                      0.0073                      -18%

The problem I have is defining the ranges dynamically with reference to SecurityA, SecurityB, #daysHistory in the pair table.
I'm experimenting with various Lookup and Reference functions (eg VLOOKUP, COLUMN, ROW, INDEX, INDIRECT, OFFSET, MATCH).

If someone could help me with fnRatioAverage, I should be able to do fnRatiopStdDev, fnCorrelation on my own.

Any suggestions much appreciated. Thanks.

-Tom