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Because they have too much source for the data, I am not sure which database I should buy, could you please advised. Thanks
Second, I just ran some numbers, and updating every six months gives you about 40% stale data. On a monthly update, you can expect about 10-15% of your data to be stale. Remember, 1/3 of US businesses fail within the first 6 months of incorporation.
There are data providers now going after twice daily updates from directory assistance, connects and disconnects, etc etc etc. That's how much demand there is for up-to-date data.
General pricing guidelines?
For the full base dataset, expect $300K per year (that includes quarterly updates). Some of them will give you the attributes specific to the business (whether a bank has an ATM, fast food has a drive thru, etc). Some of them will charge extra for that.
That probably doesn't include a good amount of URLs, and doesn't including linking data; franchises, brand databases, etc. That's all extra.