Fact 1: The cheapest 1 year validity is TRON whereby a single topup of RM10 will give you 365 days validity.

Fact 2: The cheapest starter pack with longest validity is ONEXOX. Simpack RM10 + reload RM10 = RM20 total cost (to get 28 months initial validity).

Besides just validity, if coverage and call/sms/internet tariffs is to be considered please review the list below and check their respective websites:

1. Altel (celcom infra) : 1 year validity RM28
2. BuzzMe (Umobile infra) : 1 year - RM38
3. ONEXOX (celcom infra) : 1 year RM25
4. TRON (digi infra) : 1 year validity with any RM10 topup
5. Tunetalk (celcom infra) : 1 year validity RM28
Editedt: swatting typo typo typo ...

tron coverage and plan and rates same as xiddig 
http://www.xiddig.net/

Tron has been around for many years already, just that the number of users seems to be very small.