here's one.
192 Tuas - Boon Lay.
30 Boon Lay - Bedok
24 Bedok - Changi Airport.
It will of course exceed the 2-hr limit, but you can claim the rebate the next month!
Another one!
79 - Boon Lay to Jurong East
51 - Jurong East to Hougang Central
27 - Hougang Central to Changi Airport / 89 to CACC.
1.90 is possible
i took bus from kallang mrt to pasir panjang, within 40 min, after alight, i get on another next bus, from pasir panjang to katong, from katong another bus back to kallang,
as long during this jorney did not repeat same bus number, within 2 hrs, last few trip can possible be 0 fare, same day check at machine can reflect travel detail
next day those 0 fare will not reflect on machine,
also tried, kallang mrt till boon lay mrt, shopping within 40 min, take bus 30 back till tanjong rhu, change 12 back to kallang, bus 12 possible is 0 fare
I did a West - Central - East - West in 5 hrs with six transfers for $1.90. Actually $3.80, but you can claim back the next month. It took some careful planning to pull it off.
In that trip, I found that one of my errands was delayed ie. some office was not open till 45 mins later. So to continue to qualify for the $1.90, I waited for a while and took the first bus that came for 1 stop and walked back :)
There were other times when I forgot to claim back the extra fare above $1.90 due to the time limit.