That number may be close for a double axel trailer if you don't do the work yourself. I was quoted $500 per axel by a guy in Portland. That included all parts except the in-cab brake controller which I already had. I did the conversion myself for about $250 on my last single axel trailer and it ain't rocket science.

Steve,
There was a thread a couple of weeks ago about Canada limiting surge brake trailers to 2800 kilos or about 6100 pounds. I haven't heard anything about something like that happening in the states.