Aragocrete is cheap and easy. I make mine with Portland Cement and Aragonite sand. $30 for 30 pounds of sand on LiveAquaria (might be similar on Amazon but I had a gift card). Portland Cement is $5 for a bag. I take about a cup of each, mix well, add water a little at a time and mix between each addition of water. Once the consistency is not quite fluid but pretty much a wet mud that still sticks, I "plop" it in the sand mold I made from damp Aragonite sand. Then cover it with more moist Aragonite sand for 24-48 hours, then I take it out and let it air dry for another 24-48 hours, then place it in a bucket of tap water to soak. Change the water every day or twice daily until the pH stops raising drastically, then you can put it in the tank or you can put it in aged saltwater to start seeding it.
OR you can buy rocks you like.