You know, I am not sure never hitting 50 yet, but I found LTW easy to level past the aldgoat level. Most things leather are straight up animal/monster drops, except for the handful of other class items, and you can in fact level almost purely by making leather. What I did is I farmed animal skin. Leveled purely on that until diminishing returns. Then I farmed hide, and did the same. This brought me to the aldgoat stage without spending any money at all beyond equipment repairs, and now I had several stack of leather and hard leather, which I then sold on the market for enough total to purchase alumen for half a stack of aldgoat leather. When I ran out of alumen, I turned around and sold the aldgoat leather and bought more (and still had gil left over) to keep leveling. While it was time consuming, I never actually invested any money apart from equipment repairs, and even that once I reached the aldgoat stage, I was covering with income from the ltw itself.

In terms of things that must be purchased, I think CUL is actually the worst to level, because right from the first level every single item must be purchased, unless you have a BTN, and even then they are from all over the map including la noscea so even farming yourself you have transport costs. Not to mention there are a few key items are not farmable. I never made a fraction of the money on CUL as I invested. I was spending ridiculous amounts even before level 15.