Aquarium stone

I think you may be missing the forest for the trees??
You are in a grand place to find lots of rocks! So perhaps it is more a problem of seeing what is there? Easy enough to do but it doesn't mean the rock is not there.
I grew up kicking rocks and never consider buying them! Maybe some discussion on what to look for might help.
One first point is on the rocks changing the PH. Things like aragonite, cichlid sand ,etc. will all have a somewhat "natural level" on PH. One might raise it to 7.6 while another might go as high as 7.8. But they do not add together to go higher than the higher one. So having those two mentioned and adding limestone doesn't blow the top off, it just gets to the max quicker.
Thinking of how the rock or other are degraded may help. To degrade a stone like Ohko or limestone, the water has to be at a lower PH. Limestone is alkaline, so putting it in acidic water will degrade the rock quicker but as it does, the PH rises and the effect slows. Kind of self regulating.
Since you mention African cichlid sand, can we assume your cichlids will be African cichlids? If so, I would certainly go looking for limestone as it is very cheap/free and abundant in many places.
From there it can get more complex if you want "special" looks. Much of the "fancy" stone is actually eroded limestone that comes from a specific point and somebody has given it a specific name. Sells better than way?
Texas holey rock sells for more than a dollar a pound but you can also pick it up off the ground and call it eroded limestone.
Try looking along the highways for "rip-rap". It's about as cheap as it gets. Your part of the country may use other materials like granite or marble or whatever else they find cheaper. Rocks are rocks and good old country boys should NOT buy rocks!