The Senator seat, at least the Chancellor seat grants +9% to ARPD.
However, it is interesting to note that this bonus is applied after/before the Pricing perk for cost.
Cost of Goods = ARPD * Pricing bonus * Senator Perk * CoGS
eg. 58 ARPD * 1.24 * 1.09 * 0.82 = 64.28 per unit
Cost of Goods = ARPD * (Pricing bonus + Senator Perk) * CoGS
eg. 58 ARPD * 1.33 * 0.82 = 63.25 per unit
This increases the effectiveness of the Pricing bonus in terms of cost of goods, I have not done specific observations for ARPD but I would assume it is the same.
Have fun, ST