Import old database orders in new database

I’ve recently upgraded my Magento store from 1.6.2 to 1.7.2

I did this upgrade on a local machine as the online store was still running. As an effect, I had customers making orders on the online database while I was upgrading the local database to 1.7.

Now I need to merge the orders from both databases so I don’t lose any order in the backoffice.

I’ve looked into some extensions but they’re all paid.

How can I achieve this without having to pay for an extension I’ll only use once?

Many Thanks,
Suresh Sharma