I buy metal write-on labels from National Band Company. They have a copper wire attached. The soft metal is backed by removable paper. You just write on it with a ball point pen.

The labels I use are about 1/2 x 4", but they sell various sizes.

Then I make a stake from heavy gauge wire (from any hardware store), about 18" long, with a tight loop at the top. I then attach the copper wire to the loop.

Very inexpensive. Easy. Lasts forever. Yes, a bit hard to read unless I pull up the stake and scrutinize the label.
Very inexpensive.

I recommend multiple forms of identification. Stakes with labels are helpful but have a way of getting lost. You can draw a map of your peonies as well.
Melissa