I have used copper pipes in the past and they age really pretty! I've also used just inexpensive Ikea curtain rods and they hold up well if the porch is covered.
I have used hooks into the ceiling, but you could also use a curtain rod from Walmart, Target, Amazon, or IKEA. Also, you could use metal piping!
The tension rods that hold shower curtains would also work, though the other two suggestions are good. Please post a photo of your finished project. :-)
Usually there is a long run between vertical post. Depending on the weight of the curtains when wet, I think the least expensive way may be to string cable and then hang with clips. If you need more support perhaps cut lengths of electrical conduit, it is easy to paint.
How about some pvc pipe as the curtain rod.
I used galvanized pipe & flanges for mine. Spray painted with Oil Rubbed Bronze, but you can leave plain if desired. My curtains were made from drop cloths, so they're a little heavier, & the galvanized pipe was more cost-efficient. I live in a suburb of Phoenix, & we get terrible monsoon winds during the summer. PVC would've bent & sagged after one summer.
I bought inexpensive curtains and hung them from my gazebo using shower curtain rings. They are washable and can be rehung easily.
I have used metal conduit for years. Paint color you want. I use cup hooks to hold conduit. You can put fancy ends on them if you want.