Having purchased two such homes, I have limited experience with new developments though I have some secondary awareness because friends have done so as well.
In the beginning, the builders were inflexible on the price of the home but they were willing to bend on upgrades, charging only for the additional cost of better appliances, carpet, tile, etc. without markup or additional labor charges. Early home prices were low, relatively speaking because they wanted to get bodies in quickly. The craftsmanship of the early homes was also on the higher end because a happy resident is the best advertising available - and it's free.
Thinking outside of the box can also save you a few bucks. In my previous homes, I floored the crawl space with plywood for additional storage. With my current new home, I decided to let them do it. By mutual agreement, they used large plywood scraps from the roofs, at no charge. It made no difference to me if the floor was 3x4 pieces, etc. instead of 4x8's. That saved $400 to $500 in materials as well as my avoiding my sweat equity. Another freebie ($300 value) was a tiled bench seat at the end of the walk in shower (I only paid for the nominal cost of the additional tiles).
Closer to the end, the builder offered more upgrade incentives because he was trying to sell the last dozen or so units to be able to tie up the project and move onto the next one. These were pretty much offsetting because base prices for the homes had risen for two years. One area of significant savings was on the highest premium lots which for the most part were near the last to be sold. Discounts of as much as $8k were given but that's more of a gamble because you have no idea what lots will remain available at the end of construction.
As a general rule, do not have the builder do improvements not involved in the Certificate of Occupancy. For example, because of my exterior hot tub, for safety reasons I am required to have a 5 foot gated fence around it. The builder's fee would have been 50% more than the going rate (the builder marks up the private contractor's fee). The same held true for the higher end screen door and screening in the exterior entranceway, driveway improvements (deco paint or tiles), etc.
The short answer? You can attempt to negotiate a better price on your upgrades or additional improvements. The worst that they can say is no.