One possible option would be to ask if the builder/developer is willing to sell a lot in the development to you.
If so, you could do some preliminary inquiries with other builders and see if it is a viable alternative.
Builders are not real busy and you may find the ability to realize the "custom" home you want that is designed with an end budget from the start.
Also, are you really locked on this development? There are lots available to custom design your new home on.
Good luck on your search!
I actually have clients who were in pretty much the same situation as you stated. We brainstormed and worked with the builder and now we are in the midst of having their dream home built. It does depend on the builder essentially. I have worked with some in your area and this home I spoke of is right down the road in Marshfield. Feel free to contact me at email@example.com if you have any other specific questions or perhaps I may be familiar with the builder. Good luck!
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The answer really depends on a lot of variables (the location, the days on market and how many units/homes are in the development) but as a general rule of thumb new developments generally sell close to their asking price. The builder/seller will be very strict about the purchase price because they have more than one property to sell and as soon as one property goes on record as selling at a big(ger)discount it can affect the appraisals of the other properties in the development that are under agreement and also futures sales of the properties that have not sold. Essentially it is difficult to get discounts in new developments. That said if you can be patient (and your buyers agent can be diligent) sometimes you can get a nice discount. One of my clients (at my instruction) was very patient (for about 4 weeks) on a property that was out of her price range and ended up getting a 4% discount with concessions which is pretty good. The builder cares about price so if you can come in with a strong offer price he/she will likely consider added all the appliances, closing costs and maybe some upgrades.
Hope that helps!