From A Builder Builders are sellers and their prices and terms are as negotiable as any other seller. If a builder is selling out a development quickly, your chance to negotiate is poor. If the builder is not selling as quickly as they would like to, your price and terms are likely to be very flexible.
Many builders prefer to leave the price constant and sweeten the deal with other things.
They may offer to pay your closing costs and offer you upgrades in the finish out or appliances or landscaping extras. Builders prefer this method because it keeps their sales prices stable and helps them sell their next home hopefully at the same price but without the concessions and upgrades you received. This is important with new construction because price stability is profit stability. There may be a conflict of interest. Sellers are concerned with closing the sale, not getting you the best mortgage.