Calculation wrong here.
1GB = 1000MB = 1,000,000 KB
Using your example, for Sunsurf 5 at $0.0107 per KB,
1 MB = 0.0107 x 1000 = $10.7,
1GB = $10.7 x 1000 = $10,700
10GB = $100,700!
But M1 quite "nice".. will cap this at $319.93!
For Singtel at $0.0019 per KB,
$94.16 =~ 50MB...