Does a material component cost for one component require all components involved for the spell?

Question

When a cost is listed for a component, does that mean you need all components to cast the spell or only the one with the cost included?

Guards and wards, page 248 PHB.

burning incense, a small measure of brimstone and oil, a knotted string, a small amount of umber hulk blood, and a small silver rod worth at least 10 gp

Material (M), page 203 PHB.

But if a cost is indicated for a component, a character must have that specific component before he or she can cast the spell.

Basically, can a focus be used to replace "burning incense, a small measure of brimstone and oil, a knotted string, a small amount of umber hulk blood" but not the "small silver rod"?

Answer 1

You only need to supply the material that has a cost

As you quote

But if a cost is indicated for a component, a character must have that specific component before he or she can cast the spell.

If the intent was to have you be unable to replace all of the components with a focus, it would say "a character must have all the components for the spell" -- but it does not, it just says "that specific component." A spellcasting focus can replace all the other components as normal.

Some spells do require you to have all material components on hand

However, some spells indicate that all of the material components have a cost. In this case, you must provide all of the components. For example, the MC of find familiar is:

10gp worth of charcoal, incense, and herbs that must be consumed by fire in a brass brazier

The charcoal, incense, and herbs must cost 10gp altogether, and they must be consumed by fire in a brass brazier. A spellcasting focus cannot substitute for any of the components here because all the consumable parts also cost money, and they specify the manner in which they must be consumed.

Divination is another example, which requires:

incense and a sacrificial offering appropriate to your religion, together worth at least 25 gp

Summary

In essence, the components you may not replace with a spellcasting focus are only those which have a gold cost, but all other materials can be substituted out as normal. However, some spells have material components which all share a cost, such as find familiar and divination. In these cases, you need to have all the components on hand.

Answer 2

Correct, specific components with costs must be supplied separately from the component pouch.

The rules cited in the question spell this out, and they are repeated in the equipment section:

Component Pouch. A component pouch is a small, watertight leather belt pouch that has compartments to hold all the material components and other special items you need to cast your spells, except for those components that have a specific cost (as indicated in a spell's description).

(PHB, p.151).

Guards and wards is a great example of this, as spelled out in the question. Sometimes a spell has more than one component that has a cost; if so, it will be clearly stated; for example, the material component for divination is:

incense and a sacrificial offering appropriate to your religion, together worth at least 25 gp.

(PHB p. 234, emphasis mine).