It seems like most people agree that the best masters to prepare for PhD are 1) European 2) Canadian or 3) the very few select American schools (i.e.Duke)
I had a somewhat similar profile a couple of years ago (I had a higher GPA from an unranked state school) and went to Illinois State for my masters. Here's what the masters at ISU allowed me to improve:
1) Picked up additional math courses (I had only taken up through Calc 2 before the masters, now I have the full calc sequence, probability, LA, and RA)
2) Greatly improved my LoR (before I was asking professors who I had taken 1 or 2 classes with, now I have LoRs from people I have worked with for over a year)
3) Research experience (before I had none to speak of, now I have a co-authored article in a decent journal plus a lot of experience writing scholarly articles)
4) Questions about GPA (my UGPA=3.4, my grad GPA=4.0, this helps answer some of the questions about whether I could handle grad level courses)
The results show how much I improved my profile with the masters: before the masters, I was rejected at the only PhD program I applied to (University of Oregon = ranked #59 on U.S. News); after the masters, I was accepted with funding at Michigan State (#31) and Kentucky (#56) and waitlisted at North Carolina-Chapel Hill (#34).
If I were in your shoes, I would apply to a few of PhD programs (i.e. stretches) and a range of masters. If you get into a PhD then great, if you go to a masters program you can improve your profile to get into a better PhD program.
Not that I am trying to sell you on Illinois State, but ISU does have a specific program for Peace Corp volunteers (one of the 5 largest programs of its kind in the US). So, that might be something worth looking into.
If you search the forum you should be able to find a lot of similar questions and answers as well as more complete lists of potential masters programs.