1999 Peugeot 206 My Peugeot 206 1.4 look is misfiring

Shakes or Wobbles problem
1999 Peugeot 206 4 cyl Manual 116000 miles

I am very concerned because I know nothing about cars and my little Peugeot is misfiring and also has an oil leak underneath when parked up. My husband has said there is no smoke and I have checked there is no white gunk in the oil. I am worried this is a huge problem and will cost a fortune to repair. There are no warning lights on at all. Could someone tell me what it might be and if it will be expensive to sort out please! Xx