I use the pea gravel as an edging. Here where we live we can go to a gravel pit and they sell it by the ton. You can get a pick-up box of it for $10 to 20 or if they are in a really good mood may even give it to you free.
Surprising what cash does fot the guy's beer fund.

I dig out the sod and make a trench then line it with plasttic so the weeds don;t come through It can be anywhere from inches to a foot depending on how much gravel I have left in my stock pile. Some of my areas I leave it bare with a bit of a trench and either lawnmower or weed eater close. They grow in from time to time so have to do a clean up but not really that often. If I used the black edging I would need a mile of it so would take away from my hosta fund. I found I hit it with the lawnmower and made a real mess so ripped what I had out. I also did a rock border then the trench thing and pea gravel on the outside of that but got in a rush and never put plastic under the rocks and trench so have grass growing between. Roundup will cure this for a while. Good luck with what ever you try
Faye

Rail road ties and rocks.

Course I live about two miles from a rock quarry that charges $20 to fill your truck and a really sore back loading them.

Here is my Manifesto :
I want an edge which is easily to mow on. I do not want grass to grow through an edge. I do not want to use another edger like a string trimmer in addition to the mower every week. I do not want to redo an edge several times a year, except for lets say sweep a spade blade along it once a month. I do not want to do extra work!

After looking at and using edges since 1974, for my wants a heavy duty black plastic edge has been the best. I want clean and sweeping lines and that edge does it all the times without rework. Roundup is very dangerous in respect to drifting it on desirable plants and accidentally in the rush using it wrong (I did that).
Bernd

I divided some Hostas over the weekend and put down a brick edging I found at Lowes 3 for $1. I can mow right over it so I don't have to use a trimmer, it will last basically forever, and I think it's prettier and easier to work with than the black plastic.

Rocks.

I used 6 inch by 6 inch sticks of yellow limestone.. buried like the bricks above. I can't say it was cheap, but I love the look and ease of mowing.