C# allows you to do implicit casts when you do not lose information, e.g. int to long. I cannot remember the last time I had to cast to something where I would potentially lose information.

However, I don't think manual casting is a cost at all - it's more of a guide telling you something in the design is wrong, or a reminder to make a comment of why you do it. And for any long maintanence projects, you want to catch all the bugs you can as early as you can.