My son works at a body shop as a painter. It most cases, a plastic type body piece such as the front and rear covers can be costly to repair if they have any rips, tears, or cutout pieces in the plastic. A special type epoxy is used as filler, or in the case of a tear, the piece has to be glued from the back, (they drill holes at both sides of the tear and "bevel" the sides to create a valley to prevent it from spreading), then the epoxy is used to fill in any drilling or valleys done to smooth out the surface for paint. So, all this work is labor time, and that's what can total up.
Your best bet would be to get an estimate from a good body shop that specializes in this type of work, and compare this cost against what a good used one will cost you. When buying used, price counts. Be careful of a used one that has a cheap price; it is most likely containing damage that yours already has. Maybe you'll get lucky and find one thats perfect and in your color.
Also be aware that shipping is high for these pieces as well. Some advertize free shipping; be weary of that too, as they may not wrap and package it up properly, and it could get damaged in shipping. A local yard would be your best bet; you can examine it first hand and save on shipping.
It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.