"Is sewing less expensive then just buying clothes on a shop?" is such an interesting question.
Sewists are usually say it's not, and they partially right, because it definitely more expensive then buying stuff from Shien. But here is the thing. A lot of people who sew (at least here in Russia) are not choosing between Shien (we don't have it anyway) and sewing. We sew because a lot of things we want to buy are either unavailable or very expensive.
Like. My grandma sewed because of Soviet economics and Iron Curtain we barely had any decent clothes. My mom sewed because in 90s in provincial Russian town you can't even buy fucking chicken in the store, I don't even talk about clothes. I sew because of Russian economics and sanctions we barely have any decent clothes. And also I have big boobs and I just can't buy some stuff in the stores.
So. Actually, you can sew for cheap. If your relative has a sewing machine (it's pretty common here in Russia) and you can borrow it, you don't need to spend money on your equipment. You can buy cheaper fabric in online stores that are targeted at small sewing businesses. I know places when you can buy rayon fabric for 2-3€/m.
On the other hand, when you sew, you usually don't want to do it from the cheap rayon. You want better materials and sewing techniques. You want more complicated sewing pattern. In the same time it's pretty disingenuous to compare these clothing pieces with Shien clothes, because you can't get decent linen or wool pants from Shien. If you are good at sewing and you want to compare your clothes with something readymade, it can be less expensive to sew your own clothes even if you count working hours.
So, the honest answer to this question, imo.
If you have standard measurements and you are satisfied with quality of fast fashion clothes, sewing it yourself don't worth it. If you have non-standard measurements and you want better fit and quality, learning to sew is pretty good idea. It's hard tho. You won't get beautiful pants or dress from the first try.