The Incantifier in Dragon Magazine is definitely a strong prestige class, but in terms of description it's still incredibly hard to acquire. It does cost a decent chunk of GP and XP to enter, but only initially; 120,000 GP and 4,800 XP to be precise; that's nearly half the XP needed to go from 11th to 12th level (meaning they'd have to gather half a level's worth of additional XP before actually gaining 12th-level), and by the DMG a PC shouldn't even have at least that much total wealth until 14th-level; and NPCs have even lower wealth-by-level guidelines in the DMG. A monk has about the same amount of Spell Resistance as an Incantifier around those levels, but the monk's SR grows to be somewhat superior to that of an Incantifier around 15th-level onward (max SR for monk by 20th is 30, max for Incantifier is 25 by 5th-level in the PrC (minimum character level of 16 at that point, if they somehow have nearly double normal wealth at 12th-level to afford the entry cost), and the Incantifier can NEVER gain more SR than that; the PrC specifies that their SR overrides all other sources of SR and that it is 20 + their Incantifier level; it's a 5-level PrC so maxes out at SR 25).
Incantifiers rarely take on apprentices or allies of any sort, they're paranoid, and they're hundreds of years old with plenty of bitterness and an egocentric focus. Incantifiers must be nongood in alignment, and are often rivals with other Incantifiers. PCs are incredibly unlikely to manage convincing an Incantifier to teach them the ritual and allow them to perform it. The Incantifier is obviously meant to be used primarily as a PrC for villains, just like the Blackguard and stuff. This is not in the least bit unprecedented, the DMG introduction to prestige classes (at least in the 3.0 printing) specifically states that some prestige classes may not be suitable for PCs, and are made primarily for antagonists. Just because some game mechanics are in print, doesn't mean that the reader should completely ignore the rest of the descriptions that accompany those mechanics, and which describe the intended spirit of those rules.
Now, granted, Joonaibug makes a good point regarding one aspect of the Incantifier in Dragon; for some reason they left out any description whatsoever about how Incantifiers need to eat a certain amount of magic to survive. Their general description does mention that they need to absorb magic to survive, but neglects to provide even a vague guideline or rule for that; as-written, the PrC can heal itself through devouring magic, including their own spells, but has no description as to why they need to eat magic to survive, or how much they need. There is no mention of any negative effects on them for failing to eat magic regularly, and no mention of why they would even need to eat the magic of others or of magic items; as written they can heal themselves just fine by absorbing their own spells' energy, and nowhere does it detail how or why they would need to eat the magic of others.