You ask about haggling over money.
My strong advice is don’t haggle in the early days. It’s more important to get published than to get well paid.
Just ask for a “normal fee” or “your going rate”. Later, when the editor WANTS your continual contributions, start haggling.
Find out what the top rate per 100 words is paid by that publication and ask for that. You won’t get it, but it’s a starting point.
But please! Don’t worry about haggling at this early stage. First, prove that you are a reliable and constant source of quality material, and you meet deadlines. This makes haggling MUCH easier.