I have the same opinion, especially of the rock prices. I do have a few artificial decorations though. Yet, I really like slate. I just can't get around paying the price for rock and wood. So I visited the local Home Depot and checked out the tile department. Sure enough, they had slate tiles. I picked one I liked (without the "stuff" on the back) and brought it home. With hammer in hand, I broke up the slate into a variety of shapes and sizes. I then took a small piece of fine sand paper (I'm sure a file will work also) and smoothed the edges a bit, so as not to harm the fish. Sounds toilsome, but it was ok to do while watching a TV show. I boiled the slate just to be sure and performed the vinegar test, then added the slate to my tanks in a variety of configurations. You can see the setups in the link below in my signature. Total cost: $1.97. I used the slate in three tanks and I still have a few small pieces left that I did not use. The stack of slate in the 25 gal looks better than in the pic. I already had the piece of rainbow rock, but now it has a nice bit of green algae on it, so it blends in nicely.
Another thing I have done is to buy a larger piece of wood and break it up into smaller pieces. Then I can use it for a scattered effect or arrange it for a focal point. A case in point is the driftwood in the 10 gallon. Previously one piece, I broke it out into one larger and one smaller piece. Another piece of wood is split in smaller pieces and is now in the 10 gallon (behind the larger piece), some scatter in the 25 gallon and the larger pieces are along the back of the 30 gallon.