AFAIU it is essentially mass-produced (pun intended?). The master is carefully handwritten, all the others are copies taken with an industrial (if high quality) process.
EDIT: That's not meant to be dismissive of it. It looks like a very beautifut book, and I'll probably buy one.
I suppose that if you divide up the value of a full Bible by 73 or 66, the price for a Gospel of John alone is pretty reasonable. It is certainly not practical to purchase one book alone, other than for ornamental or display purposes.
A Gospel of John alone is unsuitable for any liturgical use. Most illuminated books were pretty much understood to be placed in sacred liturgical settings, and therefore it made sense to go to that expense; they would not be shoved in a monk's drawer or a young girl's dowry chest, all things being equal.
Therefore, the illumination process would produce a complete Lectionary, a Psalter, or a Missal; speaking as a liturgical Roman Catholic, the Holy Bible is not a book we use directly for public liturgy, like at all. Bibles are for personal devotion and study. A Book of Gospels is a specialized Lectionary, and I do not know its particular structure, but it would need to include all four, for sure!
If they intend to produce all four Gospels this way, or the entire NT, that's great; I'm sure a collector would avidly follow their publication and snap them all up in short order. But for ordinary consumers, the sheer utility of an illuminated Bible is questionable at best. It's the sort of thing you'll place on a coffee table as a conversation piece, or prominently on a shelf, just to exhibit your wealth and good taste.
How elaborate or precious can it be, if this costs about the same as a typical mass-produced Bible?