Here is some sql that should work. Based on the values in the price paid column, I assume this is the unit price paid. In other words, on 2010-01-11, 1500 was spent to buy 5 items at 300 each. If my assumption is not correct, I can provide a corrected solution.
round( sum(PricePaid*qtyPurchased)/sum(qtyPurchased), 2) as 'AveragePaidPrice',
datepart(year, datepurchased) as 'YEAR',
sum(qtyPurchased) as 'QTY'