if a person orders a walker, will this be delivered all put together or not? If not, what is the cost for assembly?

No.

Call Walmart, as I have no idea.

It would probably come in a box and it would be folded. There shouldn't be any need for assembly. But if there is I'm not sure how much it would be

No, you will need to assemble the Walker. I'm not sure if you can pay to have it assembled.