Thanks all for your responses.
We would need to maintain the activity price at level hiugher than cost center, e.g. region or country. So that in case if the activity prices are not available at cost center level, system automatically read the price from higher level.
Please let me know in case there is any workaround for this solution.
The option of creating unique cost center for each country does not seems useful in our situation as we have multiple cost centers in same country due to different company codes operating in same country.
Many thanks.
Gaurav