Make Or Buy?
My first fundoshi was made from an old, soft white bedsheet. I tore it lengthwise into strips about 12-inches wide and 96-inches long (since then, I've grown to prefer a narrower fundoshi, 9.5 inches / 24 centimeters seems best for me.)
You can do this with literally any fabric, as long as it is lightweight, breathable, and has a little texture to it. Cotton or muslin work best. Sarashi is the traditional fabric.
You can buy 3-yards of any fabric and get 5-8 fundoshis out of it, so the cost per fundoshi is very low: usually just a couple dollars each.
This is my personal favorite fabric. It's breathable, lightweight, comes in several colors, and is very affordable. There are many, many options when it comes to fabrics. I recommend experimenting a little to find what works best for you.
No need to hem, no need for scissors! The edges will be frayed, but this will go away after a few trips through the laundry, and the edges will be nice and soft
If you'd rather just buy fundoshi, here are a few places online I've discovered that are in english:
Check out eBay, too, for frequent fundoshi offerings.