If u want project for exhibition so u'll hv to think for such kinda project tht can be used in many applications in daily life.. mostly gud projects r made by using microcntroller.. but as u told me its a mini project exhibition so u can select like Industrial safety measures system with sensors and webcam projects or mobile phone detection for exam hall security or at any othr place. simple RFID based wont be so gud.
For example- like a piezo sensor can be used for electricity generation by using the total wastage energy by human. when we go for gym we waste a lots of energy in making our body attractive. But that wastage energy can be used in d form of storage of charge by using piezo electric material. this typ of material generate potential difference while applying mechanical pressure on it. this potential diffference is stored in a battery. we can use these materials in a numbr of 100- 200 in difrnt typ machine to generate 500-900 watt power frm a small gym. Think such type of projects. I wont suggest u for simple n cheap projects. those cant be best in any way. I hope u understood wht i want to say..