My Decker who who also frequently has to operate as the rigger is trying to determine the cheapest method (essence if internal) to get one extra dice of initive when in VR, be it cold or hot.

Suggestions.

(SR5)

Well, at its base, Cold gioves you +2d6 (for total of 3d6) and Hot gives you +3d6 (for a total of 4d6).
What are you doing that +4d6 in hot is not enough?

Technomancers have the Overclocking submersion, but deckers don't really have anything. At my table, the only boostable Matrix initiative is AR, because it uses meat initiative and therefore wired reflexes and such apply. I mean, you could just stick in AR and save up for a tricked out Move By Wire system, but the 5 essence doesn't strike me as worth it. Keep in mind, though that 1d6 of initiative means a mere 3.5 initiative on average. You'd be better off improving Data Processing, or getting a better deck.

Need, nothing, want, everything.

Would like to get a little higher and still stay in cold.

As mentioned in the second post, a fast AR decker could always be an interesting option.

I would encourage you to play an AR emphasis decker. Your GM will love you, because you're operating at the same time as everyone else, instead of being on your lonesome Matrix adventure while everyone else gets pizza.

I have yet to see this problem in 5th (or 4th for that matter).
Every Matrix opewration we have done since 4th has been in tandem with the Meat Operations. *shrug*
It is just that some operations take longer than the meat resolution.

Yes, AR Hackers are pretty awesome. But lose out in some ways, and gain in others.