I own a property that has a cast iron sewer line that runs under the
basement floor, and I want to be able to mark out and locate where it runs
under the basement floor. I know that I could hire a company to come out
and do that, but I am wondering if there are any fairly cheap, creative, and
interesting/fun ways for me to try to locate the line myself.

For example, is there some kind of small signal generator that I could
attach to a sewer line snake and detect the signal from above with some type
of detector? -- maybe something that Radio Shack or some electronics store
might sell?

Or, are there relatively inexpensive underground pipe-locating devices that
I could rent somewhere and do the job?

Would a metal detector be able to detect a cast iron pipe under a concrete
floor (assuming that the pipe is not down very far below the floor?