Looking at https://platform.openai.com/docs/pricing, GPT 3.5 is $1.50-4 per million output tokens, and GPT 5 is $0.40-120, with plain "gpt-5" with no qualifiers going for $10/million.

GPT5 is probably cheaper in the sense that gpt5-nano is at least as capable as 3.5 while costing less, but the "normal" models are more expensive for the newer ones, and thats what people are generally going to be using.