Django Queryset to dict for use in json

I have the following queryset:

prices = Price.objects.filter(product=product).values_list('price', 'valid_from')

How can i get the prices as "json"

{"aaData": [
    ["70.1700", "2007-01-01"], # price, valid_form
    ["72.6500", "2008-01-01"], # price, valid_form
    ["74.5500", "2009-01-01"], # price, valid_form
    ["76.6500", "2010-01-01"]
]}