Easiest plants to start with are Java Fern, Java moss and Amazon Swords. There are many versions. My favorite is the needle leave version. Also check the sticky on low light plants. Check the sale/trade section of this forum. If you just want a few plants check out Petsmart. I have seen Java fern there.
Cheapest substrate is dirt with 1ml gravel, like pool filter media, over it like in the El natural section.
What size is your tank? Are you going to use rocks, wood, or ornaments?
Here are scape's you might like. Th 2nd 1 Octopus, 3rd and 4th eyebeatbadgers are at this forum.
Just google cliff at this forum and you will find more tanks with rocks. Rocks are easier to work with for you don't have to cure them, which can take a long time. You can get rocks at quarry very cheap, lanscapers or outside. To make certain that it is safe pour some vinegar on them, if they bubble/fizz you don't want to use them. They're limestone. Limestone raises the Ph. Safe rocks are granite, river rock, and slate. Lava rock, which is in the barbecue section of Home Depot, might be safe.
I am using lava rock to provide some iron for my plants. For I have made the mistake of buying plants and then the lights. Since the lights don't have a lot of red photons I have to use supplements.