Kristen,
I'm no longer building custom homes, but I built the Stoneleigh in 2007/8. It's a BEAUTIFUL house! The allowances listed all seem reasonable but perhaps just a little on the low side. If you are careful in your selections I think you can stay within budget. On the flip side, if you have expensive tastes you could easily blow the budget on each item.
Your builder may legitimately not yet know the price of the door you picked. Options like finish, caming, etc. affect the exact price. When working closely with a trusted supplier, a builder will sometimes order what the customer has specified prior to receiving the exact price. It's not to play some nefarious pricing game with the client, it's just a matter of efficiency. If vendors regularly work with a builder and know that the builder is consistently shopping their price, they will provide consistently competitive pricing to the builder.
It's not necessarily the best way to do business, but it happens a lot.
That being said, the builder could be playing a pricing game; do you trust him?
It's great that the builder allows you to shift unspent money from one allowance to another. Some builders don't. Just make sure that he is keeping (and supplying to you) good records of what is spent. It's easy to lose track of overages and unspent money.
Best wishes!
Matt
