I once had a plastic clarinet, but it wasn't a cheap student clarinet at all. I wanted to join the school band, and my dad found a classified ad about a clarinet for sale. We went to the owner's house and he brought out the clarinet and case. It looked like it was made that morning. Every key was shiny, and they were clearly made out of silver. I say it was a plastic clarinet, but it wasn't a cheap kind of plastic.
The seller told my dad that he really hadn't planned on selling that clarinet, but he joined a jazz combo that only allowed its members to use vintage instruments, like wooden clarinets. He wanted to sell the plastic one so he could have his wooden clarinet repaired. He sold it to us for a very reasonable price. I played it all the way through college.