Today see ST it cost less than $3 one way from Tampines to Jurong(bus-MRT-bus)
I think max will be $3.50 eg. Changi Village to end of Tuas(power Station).
You sure?, there is noo direct bus to Tuas Power Station only on Number 182 or is it 184 from Boon Lay Interchange, of course, you get lots of discounts changing from train/bus/bus....to bullock cart..oops!..ha ha ha