Rain chaps are a really popular alternative to a pair of waterproof trousers, especially for lightweight hiking and camping. These are my own design, all made to order, so contact me with your measurements and other requirements. Options include making the belt loops fixed or adjustable, the side Velcro strip full length or in sections, and a bag to store them in. I can also add loops on the corners so when opened out flat, can be used as a groundsheet to sit on.
The ones pictured weighed 130g and 82g respectively. This will vary on the material I use, the attachments you choose and your dimensions.
I carry a lot of different grades of Silnylon, so will discuss with you which is the best choice.