The only bar soap that can be used relatively well with a razor is Ivory. Yardley is nice bar soap, but not for twice the price. I get mine at either Dollar Tree or Family Dollar for about one dollar, and I use it to wash up with, then use a shave soap to shave with (or a shave cream).
You might be able to find a bar soap, or bath soap that is passable for shaving, however, I would never expect it to be a stellar shave. Shaving Soap is formulated for shaving, and as such the formulation is quite a bit different than that of a bath soap. The ingredients may be similar be the proportion of those ingredients will be totally different. Shaving Soap is also formulated to have a thick, stable lather. Characteristics that simply don't matter for a bath soap.