So here's what I did:
I started with some fabric, and a yard covered up enough of the board once I added the borders (click the link for the printable template). Then I used (well, stole, then used) my husband's laser level.
I had these foam popsicle sticks leftover from a project last year, so I used them. I wanted the x and y axes to be really perpendicular, so I took my time with this step. I stapled each one on the ends as I went across, then went back and reinforced them once I was sure they were in the right place.
Then I started adding cording (scavenged out of my grandmother's sewing closet) at two inch intervals. I just guessed at the length - they're uneven, but they're covered by borders, so it looks good. I marked the two inch intervals on the foam (see the indentations from my pencil above?) then just twisted the laser to meet the dot. This step was what I had anticipated spending tons of time on, but once I did the first 2 or 3, it went by super quickly. Attaching all the cording took maybe 20 mins. total.
Here's a close up of how I was lining it up and stapling. (And also the proof of how uneven these really were. Less measuring = less time spent)
Once the vertical lines were attached, I repeated the process with the horizontal lines.
Overall, I'm so happy with how it turned out. Here are a couple tips:
1. Don't use yarn for the grid lines. That's what I tried originally, but it's too stretchy.
2. It will sag after a few days. Just staple it back up, and it should be fine after that point.
Here's what I'm using to attach points.
Small command hooks hot glued to foam squares. They clip wonderfully!
(Side note - the small command hooks aren't great for graphing lines. I've been using jumbo paper clips for lines, then attaching yarn to the paperclips AFTER the paperclips are in place. So far, it's the most accurate way to keep a line where it needs to be.)
Here's that finished product: finished with borders, and book covers cut in half, then stapled up to hold the hooks and paperclips.