Not that cheap.
sent a small parcel from west to east days ago.
it weight <500gm and it cost me RM8.85.

Checked the rate on poslaju website and found the following:-
Poslaju Rates For Within Peninsular Malaysia / Sabah / Sarawak

Tariff For Weight Not More Than 2 Kg =2000 gm

Poslaju Tariff For Document:
Total Amount : RM 10.50


Note :
The above amount is not inclusive of 10% fuel surcharge, 10% handling charges and 5% GST
No 5% GST for item posted from Langkawi and Labuan.

So far, i had never encountered unpleasant experience with pos laju and Skynet

i just sent 1kg of stuff, cost me rm8.15.

because charges to east M'sia is depends on whether Sabah/Sarawak.
Also, charges to different town (KK/Bintulu/Miri..etc) may differ.