Metallic screws have been done for ages now and yield good results in good hands. In my opinion both are same. If you are cash strapped badly go for metallic one.

Let your operating surgeon decide these things for you.

Cost of the operation is entirely dependent on which hospital it is done and who does it and what implants and equipment is used. Coming to the implants, Biodegradable ones on the tibial side are very good as you get the best of both worlds. If the cost is a significant factor then metallic interference screws are just enough and will cut the cost of the surgery significantly.