Yes, resistance to antibiotics comes with a cost. There are several mechanisms for antibiotic resistance. For example, the bacteria could produce a protein that

Yes, resistance to antibiotics comes with a cost. There are several mechanisms for antibiotic resistance. For example, the bacteria could produce a protein that pumps the antibiotic out of the cell. Producing this protein is expensive, so in the absence of antibiotics, bacteria tend to lose the genes responsible for it.