Profibus is a proprietary and closed protocol with therefore stupidly expensive chips which implement it.
Modbus is a simple and open standard with loads of projects (hardware & software) floating around the 'net.
If you mention both in the same sentance, together with your question, then it clearly shows you have not done your own homework and do not deserve to waste the time of other people.
Do your homework first, then come back if you have a serious question or get stuck on some details.