What is the cost for top and bottom retainers?

Each person's mouth in unique to them. Only your dentist can give you the estimate for the cost of retainers. Sometimes depending on the problem you may just skip the bottom retainer if the person has an overbite.

This depends on the orthodontist, the area you live in and the type of retainer you want. You may also be required to pay for a new set of impressions. Have you lost or broken your retainers? If so, call your orthodontist; they should have your impressions and quote you a replacement cost over the phone.