if it's not sentimental and you have a bit of "handy-man" in you, you could probably try and do it yourself with little no problems. and if for some reason you shatter or destroy the handle, you can always try it again on another.
gettinig the knot out if farily easy and if you post a thread in the "restoration forum" you will get plenty of help and someone will most likely have restored the same brush.
doing it yourself will add a feeling of pride.
i don't know what type of restore you are doing, but unless you are talking about restore a severly cracked handle, you should be able to do it yourself with stuff you have lying around or a few bucks at home depot/lowes.
some foam sanding pads (various grits), epoxy and plastic polish (or clear coat if you are talking wood handle) is all i have ever needed to do the few i have done.
once you do one yourself, you will be hooked. i have completed 2 in the past (1 plastic, 1 wood) and have 2 more plastic ones on the go and 1 more lined up from a member and one on ebay i'm watching.
it's addictive, you have been warned....but it is fun.