You may want to give the "bargain finder" here a try. Although it would help if you had some ships in mind and a time frame. Once you post there, travel agents will e-mail you back with prices on the cruise you list. Its a good place to start. Also check out the "cruise bargains" here at Cruisemates and see what looks good for when you want to go.
Try reading through the "first time" section here as well, lots of good tips for picking out a ship, what to pack, etc.
In addition you will also want to check out the bargains that the staff has found as well as the regular classified ads section right here in Cruisemates. Expedia, Icruise, Travelocity and the others that are simuliar are great and will give you a base idea of the current going rates. Not any one site will always have the best price and the lowest price is not always the best. (Take note of that!) Look to see what you are getting for you money and make sure you are comparing apples to apples such as the same ship, date, cat cabin, etc when you look at prices. Also make sure that ALL costs are included such as port fees etc for a final cost.
What you should look for is the best "value"... not the "cheapest" price. The "cheapest" price may often be exactly that, and nothing more. You need to consider what you are getting for your $$$... and it is a complex undertaking at best. A good t/a may be your best bet to find a good value.
Bargain finder found me the best price for my New Years cruise from a TA right here in Orlando.
Yes everyone (CM regulars), I did book this with a TA other than my favorite one in KY, but she couldn't come anywhere near the price and told me she wouldn't book another cruise for me if I didn't take the price this TA gave me. I couldn't take that chance - so just once I strayed...