The company estimates that it will cost $1 billion to build a charging network in the Bay Area that may create as many as half a million charging stations.

Can I drop 'a'?

No, but you can move it to the other side of "half."
an half million

Got it!

Thanks, Avangi.
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Don't forget, AmE would be "a half million."
AvangiDon't forget, AmE would be "a half million."

How do you pronounce it? 'a half' or 'an half'?
In AmE, you pronounce the "h," like a hose." "a" and "an" are pronunced as written, on both sides of the pond.

In BrE, if you use "an," you don't pronounce the "h." "I'm searching for an honest man." (In this case, the "h" is silent in AmE too!)

As I recall, Nona said a few months back that the "silent H" in UK is going out of style. I may have misunderstood.

I'm sure you'll forgive me for repeating my mother's old joke about the Englishman visiting America, who ventured into the woods one dark night. Upon hearing an owl, he asked his American companion, "What was that?!" (answer) "It's an owl." (reply) "I know it's an howl ! - But who's howling?!"
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Thanks, Avangi.