I get queried all the time from prospective buyers about these issues. Pricing for new homes is a very sensitive issue for builders. This is why it is quite difficult for a buyer to walk into the sales office and demand a 10% or x% reduction in price when he is not represented (in order to compensate for said builders offer to pay a coop commission or referral fee to the non exist realtor) The builder will not do it. Simply speaking, they cannot without jeopardizing all future pricing for homes with the same flooplan in the same phase. It is much more beneficial to offer concessions, commissions, etc. As long as the purchase price on that HUD is what it needs to be, that is all that counts. That is the last domino that gets pushed over if you are the builder.
If you are a buyer you have a much better chance getting a realtor to go in and then get the rebate from the realtor then you do getting the builder to cut the cost of the home.