Я сэкономлю деньги, если буду ездить на метро, а не на такси.

I will save money if I ride the metro instead of taking a taxi.

Breakdown of Я сэкономлю деньги, если буду ездить на метро, а не на такси.

• я: I
• быть: to be
• на: by
• деньги: the money
• если: if
• метро: the metro
• такси: the taxi
• сэкономить: to save (money)
• ездить: to ride (go by transport)
• а не: rather than

Questions & Answers about Я сэкономлю деньги, если буду ездить на метро, а не на такси.

Why is сэкономлю used instead of экономлю?

Сэкономлю is the perfective future of сэкономить and means I will save (and as a result I’ll have saved) money—it focuses on the achieved result.
Экономлю is the present tense of экономить and means I’m saving / I save (in general), focusing on the process or habit.
So the sentence is about a future result: I’ll save money if…

How do you form the future in если буду ездить?

That’s the compound future: буду + infinitive. It’s used with imperfective verbs.

• буду ездить = I will be riding / I will ride (habitually/repeatedly)
  Because ездить is imperfective, it can’t form a simple future like поеду does; it uses буду.

Why is the verb ездить (imperfective, multi-directional) used here?

Ездить often expresses repeated, regular, habitual travel (e.g., commuting).
The idea is: if I (regularly) take the metro instead of a taxi, I’ll save money.
If you used поеду на метро, it would sound like one specific trip: “If I go by metro (this time/once), I’ll save money.”

Can I say если я буду ездить…? Why is я omitted?

Yes, если я буду ездить… is perfectly correct.
Russian often drops subject pronouns like я because the verb ending already shows the person, and omitting it sounds more natural/less repetitive. Adding я can add emphasis: If I (personally) take the metro…

Why does Russian use на метро and на такси? Why not something like “by metro”?

Russian commonly expresses transportation with на + (vehicle) meaning “by/on (that transport)”:

• ездить на метро = to take the metro
• ездить на такси = to take a taxi
  This is just the standard idiom. You’ll also see на автобусе, на машине, на поезде, etc.

What case are метро and такси in after на?

They are in the prepositional case after на when it means “by (a means of transport)” / “on (a vehicle).”
метро and такси are indeclinable nouns (they don’t change form), so they look the same in all cases.

What does а не mean here, and how is it different from just не?

а не means and not / rather than and sets up a contrast:

• на метро, а не на такси = by metro, not by taxi (choosing one instead of the other)
  Plain не just negates something, but а не highlights the alternative.

Why are there commas in this sentence?

There are two main reasons: 1) A comma separates the main clause and the если clause:

• Я сэкономлю деньги, если… 2) A comma is typically used before а when it connects contrasting parts:
• …, а не на такси.

Is the word order flexible? Could I start with Если буду ездить…?

Yes. Both are natural:

• Я сэкономлю деньги, если буду ездить… (main clause first)
• Если буду ездить на метро, а не на такси, я сэкономлю деньги. (condition first)
  If the если clause comes first, you usually still use a comma before the main clause.

Does деньги always have to be plural? Can it be деньгу?

In modern Russian, деньги is normally used as plural-only meaning “money” in general.
Деньга exists but is archaic/rare and not used for “money” in the general sense in everyday speech.

Could I replace сэкономлю деньги with сэкономлю alone?

Yes, it can be omitted if the context is obvious:

• Я сэкономлю, если буду ездить на метро… = I’ll save (money) if…
  But including деньги is very common and clear, especially in a standalone sentence.

How would you naturally stress/pronounce this sentence?

A common neutral stress pattern is: Я сэкоНОмлю ДЕньги, еСЛИ бу́ду ЕЗдить на меТРО, а не на такСИ.
In speech, the contrast often gets extra emphasis on метро vs такси, because that’s the key choice being highlighted.