Is Basic Income more expensive because work-unconditional?

Are there general reasons why a basic income would not be affordable at a level at which a conventional guaranteed income would? One obvious reason might simply be that a basic income is given to all, whether or not they are willing to work, whereas a conventional guaranteed minimum income is subordinated to a willingness-to-work test. As a result, it is claimed, more poor people will be receiving a basic income than a conventional guaranteed income, or, if the number beneficiaries is not much greater, they will be doing less work than would be the case under a work-conditional benefit system. In net terms, therefore, a basic income scheme is certain to cost more.