I have bought the Garden mix at Geo dirt. Geo dirt is west of Austin on 290. I buy it in bulk by the yard. I think it was about $59 per yard. They also have a "Thunder Dirt Which is heavier , more out of granite sand and compost and it is good for Natives. I stay away from their extra humossy dirt because it has too much peat moss in it. You do not want peat moss out here because it breaks down and becomes hydro phobic (will not accept water) if it ever gets too dry. Water beads over it instead of seeping in.

I do not know where you are in the Hill country in the hill country but I would look for some place that sells bulk soil with a good reputation. Gardenville has or use to have bulk soil. Otherwise It is building up with with compost.

I would look up a few local nursery or landscape suppliers and ask about different soil mixes they offer and what's in them as well as asking for their recommendation for your specific need. You can also ask them if you buy several yards at a time if they'll offer a discount. Compost is always a great start. Create a worm farm/BSFL bin for even faster composting. I like making my own compost over buying but if I'm installing new beds it's usually better to buy some and add some of my own. Also, assuming you don't get much rain, wick gardens, hugelkulture beds, and drip irrigation can help cut water. I have clay/clay rock soil and I've found that mixing expanded shale with a bit of compost down a foot or so then building up the raised bed a couple feet above that with garden soil/compost/expanded shale/clay works well. I would also suggest a leaf mulch or living mulch to protect the soil after your veggies have well sprouted. Watch for bugs though, that can provide a haven for pests if it gets too wet. I usually grow a living herb type mulch but I've done leaf mulches later in the summer when it was super hot. Hope this helps! :)