Boy, that does sound expensive. It was 10 years ago but I had both master cylinders and the clutch slave for my '48 Prefect done by White Post in 1997 for $158 total. That was just for boring and sleeving. I did the kits myself. In 2004, White Post did the complete job, sleeving and kits installed for a '50 Mercedes 170. The price for all 4 wheels and the master was $557, including shipping.
As I recall, they charged about the same for kits and installation as for sleeving. If still true, you can save about half by doing that yourself. Also, I think they guarantee them for life if they do the kits.
Unless they have changed, White Post bores the cylinders and installs new brass sleeves. Apple does the same but uses stainless steel sleeves. I haven't used Apple for brakes but both should last forever. And you can't say that about new cylinders. It does seem to me that the brass might make a better seal agains the rubber but I don't know that for sure.
Good luck
Bayless