Hi,
Budgeting& LTI are not required for you to implement ECM. They are seperate sub-modules within ECM. From what it sounds like your requirements are just to implement annual bonus and merit each year. If this is the case you can implement only the "Compensation Administration" section within ECM. This would be located in the SAP IMG under Personnel Management --> Enterprise Compensation Management --> Compensation Administration.
Thanks,
Imran