To get to $420, you have to not die for 5 levels. You don't have to have exactly $420, but merely hold $420.
Start With $300
Board Cost $280
Win Day 1 $290
Win Day 2 $310
Win Day 3 $340
Win Day 4 $380
Win Day 5 $430
If you die you lose $120, so it becomes almost impossible to get back up to $420. You would have to Finish Day 7
You can also achieve TGIF at the same time, though you do not need to stay alive to get that one.