Determine Cell Row Range For Datasets?

I have a large collection of datasets, sorted/grouped by rows. I need to perform some calculations against these SETS (Ave, Low, Median, etc.).

The number of member in each SET is variable (1 to NN), the number of SET Members is included in the data. Example:

Code:
3 Data Sets:
Row Set Members Price Ave
1 A 4 $1.00
2 A 4 $1.25
3 A 4 $1.50
4 A 4 $1.75
5 B 1 $4.00
6 C 3 $10.45
7 C 3 $14.50
8 C 3 $17.75

how to compute the AVE value for each SET above?

I am thinking if I can determine the FIRST Row number for each set, add the MemberQty as an ~offset to determine the LAST Row, then use an Indirect reference to compute the ave, something like:

=AVERAGE(INDIRECT("D"&A1&":D"&A1+C1)) The SET's Ave value should be added to EACH row in each SET.

I am struggling trying to point a formula like this to the First Row of the NEXT set.