Please get a Buyer's Agent before you proceed. I think that you have a very good chance of getting the new home for even a little less than the $86 per foot but please have a professional make the offer on your behalf. A good Realtor will make sure that you get the very best deal available and that you are protected in the contract. You should also get a home inspector to conduct a thorough inspection during your due diligence period just in case the home was not built well.
1st of all, Get your own "Buyers Agent" to look out for your best interests. Not all Builders are unscrupulous, but they absolutely have the contracts and variables stacked in their favor! They will often tell the Buyer Not to bring their own agent and it will save them $$$. But I have personally seen where they will then tuck that same $$$ in on the back of the contract and in a sense, they would have charged the Hm. owner the same amt. of the commission, but kept it for themselves... -Absolutely! (just one example...)
Offer the Cleanest, simplest and quickest closing offer that you can and this will help your Lower offer to gain credibility...
Good Luck in Vegas!