Brakes would more than likely be 10"[250mm]
$2-3 K is ridiculas just for an axle with brakes
a 40mm x 40mm solid axle with brakes is very easy to fit
take a heap of measurements an head down to the trailer place and have a yac , do not mention $2-3K
complete set up is only $500 and that's using the good stuff, sell the old axle on ebay to recoup some $$$$
lots of ppl building campers or offroad trailers.