A general rule of thumb is that closing costs on a mortgage typically range from 2,500-5,000 or about 6% of your loan.
The reality is that your closing costs will depend on plenty of factors including the county the home is in and the lender you chose to do business with.
Your lender is required by law to provide you with a disclosure of your closing costs estimate.
Since you are already well into the mortgage process, just ask them for the estimate. Since you have agreed to cover 50% of the closing costs, it's very important you understand exactly how much you are expected to pay at the closing.