Greenland wax can be inexpensively made at home. The most common recipe is 90% paraffin wax and 10% beeswax.
Melt and mix together in a double-boiler setup, pour into a mould, let harden and there you go.
Also personally I had good success with silicone based waterproofers for textiles.
Furthermore, Fjällräven’s wax approach is not new. Just look at the classic English waxed jacket (most famously known as the utterly overpriced Barbour jacket made by, well, Barbour).