With regards to your first point - it's not really costing taxpayers in Wisconsin $4.5B . At least for the tax credits portion, those are taxes that would not have been paid in Wisconsin otherwise.
Plus, the taxes exist for a reason. Companies rely on public goods like roads, schools, etc for their business. So if Foxconn never came to Wisconsin, Wisconsin wouldn't have had to pay those taxes, but they also wouldn't have to pay for whatever extra public goods are consumed by the factory.
Of course, in reality, someone somewhere is going to pay for Wisconsin's schools, police, etc. So what really will happen is that Foxconn shareholders (who presumably don't, generally, live in WI) will have their share price subsidized, while other companies, or Wisconsin workers, or property holders or some combination thereof will make up the difference.