Xalek - a Rank 1 Weapon (Green from vendor) will give you 62 affection each and costs 200 credits. (62 x 3 = 186 for 600 credits)
Xalek - a Rank 2 Weapon (Green from vendor) will give you 125 affection each and costs 600 credits. (This is not a good option unless you like throwing away credits)