Try getting a quote from Cruisecompete.com . This site lets you find the cruise and agents then send you their best price for the cruise. Also lok at vacationstogo.com . They can have some really good deals and you can see different cruise line prices to get a comparison of prices.
Some agents have better deals with certain cruise lines. Maybe your agent can meet the cruise line price, maybe not. Some agents will also throw in on-board credits and such.
It really does pay to check around and compare the whole package.