Transparent plastic? Then simple optical sensors won't work. Although there are some very clever sensors that will work.
This is the link I get for searching "through beam" photoelectric sensors on Mouser: https://www.mouser.com/Sensors/Optical-Sensors/Photoelectric-Sensors/_/N-axgg4?P=1z0xkhl Most of them look very industrial. Modifying that search by going up and trying some of the other branches of sensors might find what you're looking for.
Pressure? You gave us a range but you gave it in kg. kg is a unit of mass. It isn't force or pressure. You are looking to measure the weight of something? A force? Remember the SI unit for force is the Newton (N) and the normal gravitational weight force is 9.8N per kg. You may sometimes see the deca-Newton (daN) which is pretty close to "1kg force".
Normally when you ask for a pressure sensor you are looking for an air pressure sensor. Honeywell make some great ones in the $30 range. Force is a bit more complex. Maybe you need to search for "strain gauge" or "weight scale"?