You can go for a rebate and no representation - there are many brokers offering up to 2% of your purchase price back if you use their name.
Also be careful - some builders offer sizable bonuses in features and upgrades if you *do not* bring a realtor. The trick is - you need to find out from the builder ... without giving them your name so that the decision is still yours whether to bring a realtor or not.
DO NOT sign an exclusive buyers agent agreement if you're looking at new construction... don't create a contract that might cause you trouble if the builder decides not to pay commission because, say, the first time you walked through the model home you didn't have a realtor and signed the signin sheet.
Whether you use a realtor or not DO NOT SIGN ANY CONTRACTS WITHOUT HAVING AN ATTORNEY REVIEW THEM! New home purchase contracts are heavily weighted towards the builder. make sure you understand the terms. You can get certain terms in the contract changed if they are unfair, ( I've done it twice.) Really!
Oh, and don't sign away your right to a home inspection.
If you do use a realtor, they may be able to help you negotiate a better deal (builders are dealing in this market and a good realtor may have some insight.) Not just any realtor - I would look for someone with specific, recent, quantifiable experience with the builder. Might be hard to find.
Honestly, the builder does most of the work with new home purchases, but if you are uncomfortable with just a real estate attorney or you find a realtor who knows which buttons to push ... it could be worth it. Remember though - once you walk through the model with a realtor, your realtor gets paid when you buy regardless of how effective they are - make sure you choose somebody who will bring something to the table worth, say, the $9,000 commission they'll get on a $300K home...