100 DEC is actually decent if you re-invest it into rentals to try to get to Silver. As mentioned above, stacking helps.
The game currently is geared towards having people spend money on the game, but mega bucks isn't required. If you are confident in your skill level, my suggestion is to get your ECR to 100% for Day 1/2 of the season and do a 1 day rental till Gold and burn all your ECR. Take a break for 2-3 days and rinse and repeat.
!LOLZ