I wasn't convinced, but I did the maths and, well, looks like you're right:
Hiring people in to read and respond in a politically biased way to each person in the USA would take, let's say 2 messages per day for a month, so 60 messages per person, let's say 100 million actual voters you care about so 6 billion messages, let's say 15 seconds per response so 25 million hours, let's say you're hiring Kenyans because I happen to have the GDP/capita and workforce participation rate to hand, so it's about 2 USD/hour on average, so 50 million USD.
With GPT-4, and let's approximate each message as 100 input tokens and 100 output tokens, that's 0.1 * ($0.03 + $0.06) = $0.009, times the same 6e9 messages = 54 million USD.
So, yeah, looks like you're right.
3.5 is cheaper, but tends to be noticeable; from what I've been hearing (fast moving target and all that) the OSS LLMs tend to be 90% of the quality of 3.5.