Cust steel sink?

If you're talking about a stainless steel sink, it's trivial to cut a sink in half. The trick will be in getting the sink edges looking acceptable - assuming a top mounted sink.

Not hard at all. It can be done on a metal cutting bandsaw in minutes. You may end up with an ugly edge if appearance is a big factor. You can probably cut it with a jig saw, but you can be pretty sure the edge will really be ugly.

This sounds like an interesting project. I'm thinking try to leave a bit extra so that you can bend the edge over with clamps and straight edge, then carefully flatten- if you hammer, you'll have dents all over- need to squeeze it. It is not likely to turn out cosmetically perfect- ideas such as this seldom do, unless you're pretty skilled You don't say how you intend to use it/ whether perfection matters. Sometime toward the end of this piece of work, $100 might start to seem pretty reasonable. I speak from experience.

Do a search for a wet bar sink on EBay. There are a couple for under $30.00. You can cut a sink using a right angle grinder with a thin (1/16") metal cutting wheel and a piece of wood as a guide. Make multiple passes rather than one deep pass.