the major versions are:
sap business one ( less than 100 employees)
sap business by design/ business all in one (100 - 500)
sap business suite (ECC) (unlimited)
from my understanding i think sap business one will be suitable for your client, as the remaining versions are for companies who have several divisions which is not the case here. also the cost and time for a higher product increases per level. all the best!
