I mean, obviously your website needs some pretty serious traffic to even bring it up to people. Like at least 2k-10k/day to even consider it. Otherwise no one will spend their money (marketing budget money) that way.
So, assuming you have a lot of traffic to your website, you can create a post detailing your paid guest post deal. Tell them $50/post or something. You can also throw in an advert on your website for theirs if you want. That's up to you, but again, you need to have a lot of traffic to your website first. If you do well then bon voyage, go get some paid guest posts!