Wow! That seems more than a little high to me. You might check with a general mechanic shop. The worst they can tell you is they don't work on trailers.

@tiny I have a shop that does all my everyday cars and their rate is $128.00 and they are thinking about an increase. They have been in business for about 35 years and while their rate is comparable to other shops I have found that their jobs always cost less and I have never had any problems with their work.  Unfortunately their facility is not adequate to handle a car trailer. Both he and another shop recommended the shop where I bought my trailer 25 years ago so that is where it will go on Monday for an estimate-and then I will decide if it's worth repairing.

There is a store near me that sells trailer parts. They have complete backing plates with all brake parts attached. I don't know the price, but I can't imagine them costing anywhere near the price you were quoted. Good Luck.

Mike

Not knowing which axles and brakes you have on your trailer, I can't give an accurate price. If Dexter axles/brakes many places sell replacement backing plates with an example on Ebay is:  https://www.ebay.com/itm/396667062451?_skw=dexter+trailer+brakes&itmmeta=01K1M8J1GNER9DT353FJECMMGQ&hash=item5c5b3308b3:g:vAoAAOSwaDhnyVVw&itmprp=enc%3AAQAKAAAA8FkggFvd1GGDu0w3yXCmi1fjQW3JVvX4ovNky8jEB53iGJ%2FchcaTWlqw23Gzz7oIff3TBIJft830Wg%2FRDWT0GhacAYhRnt8gPl7seHkTknpZoPncPLIc1EuAgPZkn8C4TpAgW%2FgcxIwGP8p2JtS%2BkE%2FPZqlLwkq5Vi0nH3NBnvPfjHncgUI02idGpsxW2WuPd6Mz99n2C4njRDinF9O1VBKv2XyUJBajypiFG6n%2BJybOpajO0ED0OzHlD1MQtF5C0KeML3SXk5ihKBMOKI8fneNKJE6l2DDz6c8Jr5glx25wFqIV8Ndr6rAsQ0fJcojxYw%3D%3D%7Ctkp%3ABk9SR76YyIiNZg

That makes the parts less than $ 200. The labor to replace all the backing plates on two axles should be less than a couple of hours if the mechanic has any skill. So $ 500 should be in the ball park to get the job done. That includes repacking the bearings.