Now, in terms of plants, I grow a lot of mine from seed. Some grow fairly easily, while others are a bit trickier to do, but generally speaking it is the most economical way to obtain large masses of plants ($2.00 for a packet of 500 seeds, while a young plant costs $5, and a mature plant costs $15-20 if not more). I utilized the wintersowing method as a foolproof way of starting seeds (
http://www.wintersown.org/ as well as check out the gardenweb wintersowing forums at
http://forums2.gardenweb.com/forums/wtrsow/). This method utilizes leftover soda pop bottles, milk jugs, takeout containers and other recyclables to create mini-greenhouses for seeds. Works like a charm, and lends to basically hands-off seed sprouting into young plants.
I like starting plants from seed, but it does take them a while to mature since we have a shorter growing season. In Texas, you might be able to get bigger results the first year from seed than myself, since many plants take a while to mature before they start blooming or gaining mass. Grasses are a nice one to start off with - I planted a club soda bottle with switchgrass just a week ago, and they're already obtaining their second set of leaves. Understanding the individual needs of plants is important - I usually will read up on a species before I decide to get it. Nothing in my garden that's super fussy, requires constant water, or doesn't perform well. I love plants, I love gardening, and I love horticulture, but I don't like to baby plants for very long.
Now, in terms of obtaining adult plants, I know that there are a lot of gardeners who divide their plants. There's sometimes only so much real estate in their garden beds, so you might be able to obtain free plants from them. Check the free section of craigslist, or the farm/garden section for people either giving away plants, or selling them cheaply. Sometimes botanical gardens, garden clubs, church sales, farmer's markets, and other organizations will hold plant sales for 50-30% of the price of what you would pay at a bonafide nursery. (Note that I do encourage the support of local nurseries, especially for some of their cooler and exotic plant species. I'm just not going to buy 20 pots of Feather Reed Grass from them at $10 each when I found 15 of them at sale at the local Hy-Vee for $1.50 each)
Lowe's usually has a sale rack for houseplants, and in the summer they have a sale rack for garden plants as well. I found some $19 Magic Carpet spirea plants for $1 each this past weekend. Granted most of these plants will be in less than optimal condition - don't fret! Usually just a bit of a trim, giving it a proper home in the ground somewhere, a week or two of watering and some time will help it to spring right back. I think most of the other big box stores will have a sales rack somewhere, and I usually scour it to see if there are any plants that would fit my needs there. Don't be afraid to spend money on good plants either. Sedums, for example, are really hardy and easily propagated (you just stick a stem into the ground, and it will root on it's own. Bam, two plants with minimal effort). I bought four plants, which have now multiplied into close to 100 small sedums this year.
It might take a while for your landscape to get it to where you want to. I understand that things are getting really hot down there, and it might be all you can do just to keep cool and out of the sun! You might be able to get more accomplished this fall and spring when the weather cools down a bit. Take your time and enjoy the journey!