To reiterate, silk plants are really cheap, the fish love them, and so will your wallet.
I can decorate a tank for about $3 using silk plants purchased off season at the craft store.
I get them for 90% off, which means that I pay about .30 for a bunch of plants.
Here's a tag from a bunch of larger plants:

Here's a finished plant ready for the tank:

Here's how I do it. Firts remove the base used by the florists and crafters:

Next shove a bunch of the stalks through a hole in a rock and put a zip tie around them to secure the stalks together:

Finally bend out a couple of the stems to keep the bunch from pulling back through the hole and then pull the whole assembly tigh to the underside of the rock.

Viola! You have a nice plant that looks like it's growing out of, or behind a rock. Plants are very sturdy this way and can be repositioned easily.

Finish off the look by hiding the bases of the stems with some small rocks. They'll conceal any zip ties used to attach the plants.

Plants come in a wide variety of shapes ans sizes, so let your imagination go wild:

This method of decorationg is not only cst effective, but it can cover a lot of room in your tank, creating nice habitat for your fish.

Enjoy,
Kyle May