There are two verbs in the sentence. The verb began is in a form of "past tense" indicating the action of "begin" occurred in the unknown past, and the other one is in a form of "gerund" indicating the object of the transitive verb "began" is the gerund itself and at the same time it takes "money" as its "own object".
There are clear distinctions between "began" and "spending":
- The most notable one is "began" as a main verb can change its form to all tenses assisted by auxiliary verbs (be, have, will and so on). That's why it is called an "finite verb". However, "spending (gerund)" can't change its form as freely as "began". It has only 2 forms, one with "-ing form" and the other with "having + past participle" form. For example:
I regret having said so.
Its past tense form only indicates the action of "say" occurred before "regret". Gerund can't express any other tenses in the sentence. That's why it is called "infinite/nonfinite verb"
- "began" can't be subject/object/completment without changing its form to "to-infinitive" or "gerund". However, "spending" can be any of them. That's why you can use "spending" as an object of "began". You can also use "to spend" as an object of "began".
However, there are some similarities. For example, "began" as a transitive verb can take an object in various forms such as "nouns", "to-infinitives", and "gerunds" which all have a "nominal" characteristics. "Gerund" depending upon the verb before "-ing" also can take an object in various forms as in:
I began enjoying skiing.
There are 3 verbs in this sentence, "began", "enjoying", and "skiing". Here the gerund "enjoying" is taking another gerund "skiing" as its object.
Let's take a look at another example:
I began to regret starting to smoke a cigarette.
Then, how many verbs are there in the above sentence? There are 4 verbs, "began", "regret in a to-infinitive form", "starting in a gerund form", and "to smoke in a to-infinitive form". All the above 4 verbs have different functions in just one short sentence.
Began: A main verb of an independent clause in the past tense.
To regret: An object of the verb "began" taking "starting" as an
Starting: An object of the verb "regret" taking "to smoke" as an object.
To smoke: An object of the verb "starting" and taking "a cigarette" as an
It is wrong to say spending is just an "object" of "began" as "a noun" because "a noun" cannot take any object without help of "prepositions".
Some grammarians coined a word "verbid" to differentiate "other verb forms" from "main verb" as defined below:
a nonfinite verb form; a verbal; an infinitive, participle, or gerund.
Conclusion: There are 2 verbs in different forms. Answering the question of "what is the verb here?" largely depend on "what verb" you are looking for.
- If you are looking for one "main verb", it is "began".
- If you are looking for finite/infinite verbs in whatever forms including "verbid (or gerund)", they are "began" and "spending".
It might be wrong to ask, "What is the verb here?" It would be more appropriate to ask, "What is a main verb here?" or "What is a finite verb here?".