Conditional pricing seems like it could work for this fine. You could set it up as 3 separate attributes:
And, then make a conditional price table, with conditional price based on package size.
Depending on your sample size, and how many brands and package sizes you have, you might also consider collapsing brand and package size into a single factor (attribute), if you want the ability to include the 3-way interaction effect among brand + package + price. But, that's icing on the cake.
Conditional pricing is, in my opinion, probably MOST used when doing FMCG studies and brand + package + price, so I'm surprised you don't think it is discussed much in the literature.