By the time you buy the plywood, the mortar and make the beds you will have invested as much time and energy as you would if you bought fir 2x10s

My raised beds are made of old waterbed sides ... 1 1/2 inches thick clear pine 10 inches tall, untreated.We pounded in a 4x4 post at each end and screwed the sides to it. It's been 9over 5 years and they are still holding dirt.

If I make more, I will use ordinary construction lumber 2x8 or 2x10s

Cedar is quite expensive. Pine doesn't last.

If you use cinder block, it shouldn't cost any more than buying forms and concrete (I assume you already have the river rock?)

I've got cinder block beds and the block was very inexpensive because I bought it from the brick yard and purchased a couple of pallets of "seconds". They had flaws and chips, but work great for raised beds.

Also, if you are in an area with any farms, put an ad on Craigslist that you are looking for galvanized or rubbermaid water troughs with leaks and holes. They can't be patched, so you can sometimes get them for free, just for hauling them away.

I've got three of these raised beds. This one for tomatoes is 6 feet in diameter and 15 inches high and the other two for herbs and peppers are 8 feet across and 18 inches high.

I got them for $5 each at Wall-Mart on clearance after Labor Day. This bed with tomatoes is 3 years old and still strong.

I was starting a new raised bed and was looking for a free source of organic stuff to compost to fill the bed since my soil is hard clay. I saw a tree service trimming limbs from beneath power lines near my neighborhood. I had read that most would deliver wood chips for free, so I stopped and asked. That afternoon, they brought me an entire truck load of wood chips. Because they are trimming limbs and saplings, there was lots of green leaves and twigs shredded in the mix, so it has heated up nicely and began "cooking". I've seen some people complain that the wood chips are in too big a bits for their taste. I never really worried about big bits in my finished compost, to the larger chunks don't bother me. It ranges from fingernail sized bits to finger sized bits. There are a few chunks mixed in that are the size of my hand, but not too many. After it cools down in a week or so, I'm going to top it off with a few inches of composted leaves and grass clippings that are few months old. I've got a bunch of strawberries growing in pots that I'm going to transplant so they will overwinter better than in pots.

The pots they were growing in were free as well. I buy Folger's coffee in the 2 pound plastic cans, which I save for plants. I punch holes in the bottom for drainage and one hole near the top lip. I take 2 of the plastic coffee cans and loop a nylon wire tie through the hole near the top of 2 cans. I then hang the pots over the top of the chain-link fence in my backyard. This gets the pots off the ground where my Beagle don't bother them on the inside fence, and rabbits don't eat the plants on the outside the fence. If I'm careful where I punch the hole at the top, the cans hang so that the labels barely show, and they simply look like pretty red pots.

Is that a child's swimming pool???? Did you cut the bottom out before planting?