I have used Sabiha Gokcen sevetal times. Air Arabia flights basically arrive at midnight, so I have to spend the night at the airport. The soft seats (3 in row without separation) are situated in lobby surrounded by offices of the rent-a-car companies. This area is somehow secluded from the big arrival area as space and thus offers relatively good conditions for overnight sleep in airport.
The airport is not busy in general and the competition for sleeping space is not so intense.
The direct bus Havas (to Istanbul center) sells its tickets on 18 TRL these days which is +3 TRL increase compared with January 2018 and +5 TRL increase compared with August 2014. The inflation spike still works in favour of the foreign tourists.