Up to any amount, provided they are: Ordinary and necessary, Reasonable in amount, Paid for services actually provided, Paid for or incurred in the tax year. And the "any amount" has a limit beyond which you are found to not be operating a profit-seeking business.
(Those are the fairly standard tests for all business deductions, only the third is at all specific to wages.)
There's no way to "make money" by incurring additional expenses and deducting them. If you have $100 in deductible business expenses and your marginal rate is 35%, you are paying $100 in expenses and getting back $35 on your taxes, so you're still out of pocket $65.
(Those are the fairly standard tests for all business deductions, only the third is at all specific to wages.)
There's no way to "make money" by incurring additional expenses and deducting them. If you have $100 in deductible business expenses and your marginal rate is 35%, you are paying $100 in expenses and getting back $35 on your taxes, so you're still out of pocket $65.