I just started in Riverview, and purchased an empty lot for around §2000. Before the clock actually started ticking and there was still the option to go back and play with another family (as this is how I interpreted "Before you begin playing" in the ruleset) I tried to use the family funds cheat twice in different files to bring funds down to 7000, but it wouldn't work. So I hit the tick and let them actually load onto the lot at 8.00 AM on Sunday, then paused and used the family funds cheat, which worked fine.
Is this the right way to be doing it? I hope this all made sense.