How bad is the damage? If its just a crack or a split. Just repair with fiberglass on inside. YOu will of course have to clean up the repair area first. Sand affected area on the outside of the bumper fill with kitty hair (fiberglass bondo, green in color). sand and finish with light bit of bondo if you cant get the scratches out from the sanding of the kitty hair. Id personally sand the whole bumper down till you hit the fiberglass. Primer.... and wait till you need to place it on the car before painting. Its probably just gonna get scratched up sitting in the garage anyhow. Store it out of the way.
its fairly easy to fix a fiberglass bumper or panel. just a matter of prepping the area, having the fiberglass and good resin. and knowing how to lay it down. after that its all about just sanding it out and bodyworking the spot.
the great thing about fiberglass is you can repair it right, add new sections that may have been lost due to damage. etc, and its just like new. your just addings new material of the same type, not like repairing a piece with something that it isnt made of. reminds me of a guys bumper that was a plastic/non fiberglass bumper, that had a couple sections repaired with fiberglass, and some carbon fiber overlay on it... not even a year later, the overlays started to peel up from use and sun heat.
Well, If you go decide to repair it.. clean out the old crap work. Get rid of the previous work. Go price out some materials. i think you might find its cheaper than you think. The big cost will be your investment of time. Worth it in the long run.