For Bing carb parts, you probably aren't going to do too much better than the prices you've seen .
The parts are pretty much specific to this use .
One word of caution, there have been reports here by members, that non-Bing diaphragms can cause problems, by not being as pliable as the Bings, they are a thicker material and this is one of those cases that stronger, thicker is not a step in the correct direction .
MAC is about the only cost effective replacements for the header pipes, don't know anything about them, but some members here have installed them, can't remember if they had any fitment issues with them or not .