Took my Nishiki Sport(spent the least money on my hybrid, of my 4 bikes.) Took to my favorite bike shop. They told me crank is a 'unified,' crank; can't change out chain rings. Shimano 100 GS. Crank is aluminum and teeth are worn. Need to change chain. Bike costs about $450 new in about 1994. Crank costs over $100. Is it worth the repair.? Do I have to pay that much for a new crank.? Any suggestions?