I also have trouble getting at the weeds, of which there are many in this fertile environment. I had thrown the border together using 2 x 4's and some screws, making what appears as an out of place door frame. But it was very inexpensive and enough to sell me on the idea of raised bed gardening. I don't use treated wood anywhere in the garden. Whether the chemicals stay in the wood or leach into the soil, I don't feel comfortable having such materials around, most especially when dealing with vegetables, and edible herbs and flowers.
Some people use large bricks and other pieces of masonry, even rocks for the border.
Frames and other garden accessories made from recycled plastic are also available online. When practical, and I have the time and energy, I like making things myself. Next year I'm going to try building with cedar, which is naturally rot resistant, besides smelling great. But I have nothing against using kits either. There are cedar frame kits available online at a number of sites.