If you pass around the Island (Ctrl + right mouse), you will see at least 2 lots that cost 5000$ or less. Move your family there, use the motherlode cheat to increase their funds, pull them back to the Family Bin, and you can now buy any lot you want...

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The problem is, that you can't build new lots, only "destroy" manually the existing ones, flat the terrain, and build a house according to your taste.