Is it affordable and reasonable to create a tub using tile
My speculation is the reason you can't find resources for that specific approach is because that approach is inferior in almost all ways to modern tub construction.
Most importantly: tile and grout is mostly water-tight; fiberglass or cast-iron tubs are entirely water-tight. As you probably know, any amount of regular water leakage into unintended areas can cause huge problems. This is why tile and grout is fine for areas with indirect water (e.g., tub surrounds) - though this still should be backed by a water-barrier (e.g., Redgard) and concrete board. Even when you see tile and grout shower floors, these are always underpinned by a &quot;shower pan&quot; - which is 100% water-tight. Tile and grout is, to some, a better aesthetic choice, but it is worse in the practical considerations of water control.
There are other, less critical reasons that it is avoided: one, it's generally more expensive to manually tile and grout anything than it is to purchase a prefabbed, mass-produced version; two, the curves and smooth presentation of almost all tubs is much more difficult to accomplish with tile and grout; three, a smooth fiberglass wall is much more comfortable to move your bare skin across than tile and grout (ever try and slide across your kitchen floor on your stomach?). All of these can be mitigated with highly skilled craftsmanship, but that's much harder to find than a tub at your nearest hardware store.
You do see tile and grout approaches in some large-scale water containers like public pools or spas, but even these are almost always built on top of concrete and dirt (where the small water leakage is controlled or irrelevant). Here the tile is for aesthetics and durability (a porcelain tile will wear down much slower than a concrete wall due to its hardness).
To summarize and directly answer your question: it can be done, but it will be far more difficult of an approach than any standard method because the installation will be customized and extra considerations will have to be taken to control the water. At the very least, it should use porcelain tiles (more water-resistant than standard ceramics) on top of Redgard/Redgard-equivalent on top of some kind of water resistant substrate (concrete forms, concrete board, shower pans, etc.). The last part will be the most difficult and particular part of the process, as standard construction materials will not adhere to a typical bathtub shape.