One of my co-workers gave me a plastic box that held hair colorant. She thought it might make an interesting mold. I totally agree! Hopefully it will produce interesting eye shaped soaps.
Also I love my plastic storage boxes from Staples. The largest one of the three tiny boxes holds 1lb of soap exactly if I keep my water to 30%. I tried them without lining, but I think at least a strip of freezer paper to act like a sling makes for much easier unmolding. The largest cost $3. I haven't tried the 2 smaller sizes yet. They might be more tricky to unmold.
Who needs fancy smancy expensive molds when there are so many other things that can be used as molds.