Ask up front what the fee will be. Price is only part of the picture when making an offer. A seller may accept a lower price if your terms and mortgage information may be more desirable. Try changing closing date or initial deposit instead of price. This gives you a much stronger negotiating position.
Banks usually offer lower closing costs than mortgage brokers.
Their requirements may be more stringent but their costs are usually lower. Always ask for a good faith estimate. This allows you to compare apples to apples. Try a bank first. Although every loan has a variety of fees involved, you need to compare good faith estimates.