To better understand what you're paying for, breaking down the cost, makes it easier. Looking at it on a "per pouch", or "per tub" doesn't make sense when you start to look at how much fibre you're actually getting, and looking at the cost per gram of fibre, a lot more will be cleared up.
When you compare Fibes Co. (Which costs $0.18 per gram of fibre, or $56 per pouch), the results make a lot more sense. Fibes offers 4 premium, studied, fibre ingredients. This is significantly below other high quality options, while maintaining a good diversity of fibres.
For starters, greens powders, whose benefits largely come from increased fibre, cost between $1.20 to $2.33 per gram of fibre. A very high premium for low dose and low diversity.
Supermarket fibres often also come across as cheap and accessible, however, again, when you break it down to a cost per gram of fibre, they often come out between $0.35-0.85 for diverse fibre blends. Meanwhile cheaper supermarket options are generally single source, not offering the fibre diversity and at the high quality your system needs.
Fruits and vegetables: These offer many benefits, and whole food options should always be considered. However, when explicitly trying to increase your fibre intake, the price will rise quite quickly. For example, the highest fibre fruits, eg. passionfruit, raspberries, will cost around $3-4 per gram of fibre. For someone trying to explicitly increase their fibre intake, this may not be the most cost effective route.