Have you sold your car? or are you planning to retain it. Getting a used tappet cover is not so difficult, but will cost you about a grand if they are really rare. Getting it welded will only be a temp solution. Last but not least, there are other owners who are still in love with the Palio 1.2 despite its less power compared to the 1.6litre.
Is this what which is cracked in your car?
Here is a link to a mild restoration that I am working on right now on a friend's FIAT PALIO 1.2litre. The thread might give you an idea on part costs, maintenance etc. Also if you have any info to help me out in my restoration please post the same on that thread. www.theautomotiveindia.com/forums/technical-zone/13895-quick-service-forgotten-fiat-palio.html