The licenses on Crazy Taxi are awarded using the following system:

No License: $0.00
Class E License: $0.01 to $999.99
Class D License: $1000.00 to $1999.99
Class C License: $2000.00 to $2999.99
Class B License: $3000.00 to $3999.99
Class A License: $4000.00 to $4999.99
Class S License: $5000.00 to $9,999.99
Awesome! License: $10,000.00 to $10,999.99
Crazy! License: $20,000.00 and over