I am invited by a company to see if we can work together in the future,

Hello,
but I only got a 30 days visa and they want me to stay at least 3 months. Any extension or transfer to work visa possible within the 30 days of my visa validity? Can they issue provisional overstay prof or wo the application be proceeding before the my via expiration date if I go in the first days to the immigration office Or do I have to comeback in my country? What are the costs? Thank you