There is no need to buy beef tallow (or pork lard). Your butcher is probably throwing out all the fat scraps. You can get them for free or almost no cost.
When you get home, divide the fat into small plastic bags, and store in your freezer. Here’s a beautiful free piece of fat I got from my butcher:
Cut up into little cubes, and throw into cold pan
Crank up the heat, and the cubes will melt down to make tallow
When the cubes look like they are starting to get too brown, and possible burn, scoop them out with a slotted spoon. Process is complete, you just made tallow in less than 10 minutes.