Sponsoring an H1-B employee, in theory, is always more expensive than an hiring a local because not only do you have to pay an H1-B visa employee the same wage as a local you also have to pay the lawyer and visa fees. Often times employers will also have to provide an employment contract guaranteeing x number of years of employment in order to increase chances of visa approval.
In practice, this is not the case. H1-b visa workers have poor mobility and little recourse when employers cheat the system by providing lower than market pay and requiring the employee to pay their own H1B visa fees. Furthermore, there is little (if any) enforcement that the employer seriously considered domestic applicants at market rates over the H1B applicate. 99% of the time the H1-B is already hired and the employer is posting a job 100% tailored to that H1-B applicant.