About $200 for a torsion spring. Don't know about materials.

You "could" do it youself as there's only a few things that could go
wrong... it's only a spring right? The worst thing is that you lose
your grip as your tightening it and whap yourself in the chin and lose
your lower mandible and have to eat from a straw the rest of your life.

Then there's always death, but that's not as bad as losing your lower
mandible. My opinion though.

HIRE IT OUT, and ask around if the price really bugs you that much.