Kindly note the following things:
1. First determine how good the blog is that you are going to write for. Because if it's not a good one, chances are that they won't be paying you more than pennies. Moreover, if you give them a fair rate (which is going to be above $100/$150), it will put them off.
2. Secondly, determine what your responsibilities will be. Talk to them in a clear and concise manner, so both the parties (you and the blog-owners) will be on the same page. Will you be writing *and* publishing the post? Does the pay also include using your social media connections for traffic and promotion?
3. Ask if you are going to get a byline. As you mentioned you are just starting it, it is extremely important you get one. If you do, you may compromise on the rate a little bit. It will help you in the long-run.
4. Last, but not the least, I would recommend you to be the expert and recommend them a different strategy. I don't know exactly what your deal is, but it seems you are going to write only 1 blogpost per month. If that's the case, you should be very careful here. You see, they are thinking of generating traffic with blogposts. But one blogpost per month isn't going to do that. Only after a couple of months, they will drop the idea, saying that you couldn't achieve what they expected you to achieve. In a nutshell, you should be involving with successful projects, shouldn't you? One good blogpost per week is the minimum here.
Source: I'm a professional freelance writer with hundreds of projects with my name. I know what I'm talking about. I also teach a lot of aspiring freelancers on how to get started. So do give my advice a thought.
Good luck with your gig. I hope it turns out to be really good for you :)