Price by weight and item

I have been asked to look at building a site for a grocery store that delivers it's goods.

The sell organic goods, and they sell juices by the bottle or carton, and they also sell fruit and veg. The juices will have a per item price, and the veg will be sold by weight which determines the price.

I know how to do the price by item, but how do I also tackle the price by weight in the same cart?

I have the latest eCart (but have never used it) and I also have the PowerStore 2. Could I take the PowerStore and modify it with eCart to suit my needs.

Any advice on this is appreciated.

Also, I need to make a delivery booking system... is that another thread?

Thanks.