I removed the grate from my cast iron floor drain (in basement) and
found that the internal cap (mushroom shape) had rusted off and was
just sitting in there. What's left is the cup with the pipe in it and
the grate. It looks like the trap is in good shape as there is some
standing water visible in the pipe and there is absolutely no smell of
septic gas.

My question is this - if this drain is in an old shower stall that I
want to use while remodeling the main bathroom, is it ok to use as is?
Water seems to go down properly and I got an initial estimate of $350
to replace. I don't want to have to remodel this bathroom so that I
can remodel the other.

Thanks in advance...