I would second Euphemism's assessment that Blood should be about right for a Major Focus.
Remember, a Major Focus should be less than half a Form; a Minor Focus less than a TeFo combination. Note in this sense that "self-transformation" is, roughly, those MuCo and MuMe effects with R:Self, plus a very few other effects (e.g. CrCo/Me characteristic improvements, and the occasional PeCo/Me effect to remove "unwanted" aspects of oneself, such as weight or a memory). So, it's fair to say that it's less than a TeFo combination.
Blood involves Corpus and Animal -- pretty much all Techniques. It can also cover a handful of applications of other Forms (e.g. the scent of blood is Imaginem, and a ReVi spell to concentrate the vis in a dragon's blood into a single droplet of it is also covered), but let's ignore that. I'd eyeball human blood at less than a quarter of Corpus (so it's small enough for a Major Focus, a bit less than a quarter Corpus and a quarter Animal), but not less than a tenth: many Perdo effects can be worked with blood; a significant fraction of Intellego ones; a few Muto, Creo, and Rego ones.