Most affordable? Uhmm, I think Wildfire lah (RM1,199) Even CSL oso got Android now (RM1,099) but the camera quite teruk lah no AF somemore. Between those two, I think Wildfire better - newer OS, camera got AF with LED flash, only the reso quite lame.
If can spend somemore I think Samsung's Galaxy i7500 (about RM1,399) is nice. Quite old model and very difficult to get now. OS is ver 1.-something, but I think upgradeable. The screen is AMOLED. Cheapest AMOLED Android I can think of, and picture quality is dam good.
Was walking around Digital Mall yesterday, and was told by some dealers than HTC's Android ver 1.-something phones are being "recalled" and discontinued. No stock for Magic, Tattoo and Hero. So the most affordable from HTC would be Wildfire, which they had no stock oso 'coz selling like hotcakes

If you don't mind going to SG, I think got more choices there some models may be cheaper, but warranty is SG local.