It wasn't that much of a stretch. There was a moment of panic when I realized we hadn't thought through the fact that tearing all the walls down would ultimately be necessary for running electric up to code. That was definitely an added expense up near $800ish (so. much. joint compound.)
Also, as we began to fall in love with the space, we began to justify a few indulgences, like installing subway tile floor-to-ceiling on the range wall and picking out a statement sconce from Schoolhouse Electric for the center of the room. We also backed ourselves into a corner with the faucet purchase. Long story short, there were only a few options that would even fit in the height we allotted for it. And they were pricey options.
Also, as the space neared completion, we spent a few extra bucks on details like trying to match the living room baseboard with salvaged trim (rather than installing blah contractor baseboard) and deciding to give the back landing some TLC with new tile, paint, and a chandelier, an extra couple hundred bucks.