Date Change

I am a senior Citizen living in the USA. I recently moved the dates on 2 round trip tickets to India for myself and my wife. I baught the tickets at the begining of April for about $1500/ ticket through Cheapoair A date change on the ticket from September to October cost me $900. This is not peak season I misunderstood the reservation specilist and thought it was a total cost of $450. To my surprice I am told that they charged me a Penality of $250 per ticket and a fare diffrence of $200 per ticket. Does this amounts sound right ? For a retired  person like me $900 for a change of date is very steap, it is nearly the price of a ticket. I feel these charges are excorbitant and unaffordable. I really doubt if I will ever fly Lufthansia again or book another ticket through Cheapoair.