The cost of building a lot.
When I finish of my lots, I'm never really happy with the total cost. I always try and make more interesting lots, that a family starting out with 20K simoleons can purchase without cheats. (I personally cheat all of the time but I recognize that most don't.)
So in order to get around the costs I do a little trick that'll bring the cost down by around 5k.
Place a sim on the lot you just created, turn off all decay and aspirations using the codes, and let him live for a year(4 seasons), and kill him off when the value of the lot stops falling.
What's sad is if you move a sim out, that means that the kitchen and bathroom fixtures will be sold off, and the price of the lot will go up. Killing the sim brings the value down about 100 simoleons, and you can delete them in build mode.
But sometimes the deleted dead sims show up on my lots, and that's why you might see an urn.