If i were still living in Tampines, i would take 3, 17, or 21 and drop outside downtown east.

If i were living in most other places in Singapore, i would take 3, 6, 12, 17, 21, 354 or 358 from Pasir Ris station, and stop at downtown east.

This guy i know very well usually walks home from pasir ris MRT. He usually walks to pasir ris park from home too. But dunno if walkable distance + walkable distance will = walkable distance. He only tried it once. He thinks it might be further than Buona Vista to NUS.

And if i'm not wrong taking a cab will cost less than 4 bucks.

Anyway, if you guys want we can meet at pasir ris MRT then decide how to go.