Check with building material suppliers near you, especially ones that cater to concrete rather than lumber. There is a quartz type of around 1/8" grain size, that is also sold as "natural" aquarium gravel, and is usually under $10 for 50lbs. I was told that the gravel was used to fill holes that had been core drilled.
calculators will give you the volume or bags you need for the depth you desire, and are extremely useful, for people new to the hobby, not to mention the old foggies like yourself.
It all depends on what kind of planted tank you want, and what you want to do within the substrate, ie add some other medium for your plants such as peat bricks, etc. or are you going to slope it from back to front, side. Rocks, etc.
Use the calculators as a base, and then add a safety margin when ordering. Order online for bigger tanks, that's the cheapest way to go.
I personally like to have 2" at least of substrate for planted tanks regardless of size. Check the plants you desire to have for the depth they need.
If you don't plan to have plants planted in the gravel, you don't need much at all. Some prefer the maintenance free and aesthetics of a bare bottom tank.
Now if you're keeping cichlids, heck, plan on making several trips, and plan how you want to build your rocks. And in this case it will be rocks.
So, what exactly do you want to keep in this tank? That should be the first question, for experts and nubs alike.
I decided to go with 2 Forty pound bags of pea gravel. It looks nice.
It gives a variety of colors and is quite natural looking. I rinsed them as well as I could, but even then....it clouded up my water a bit.