250 affinity between exchanges
so it would be 250 then 500 then 750 then 1000. It appears to only go to 1000 but I only tested this on Piper.
[Edited by WitnessME, 11/12/2015 3:05:41 PM]
Can confirm the 250 theory. Paladin Danes started speaking right after setting him to 260 and jumping into power armor to get regular affinity points.