Learn Finnish: Meidän pitää tehdä budjetti tänään.

This is the golden rule for obligation verbs like pitää (must / to have to). The person who has to do the action is always put into the genitive case. Instead of "we must", the Finnish structure is closer to "of us it is required".

Why is the verb pitää in the 3rd person singular form instead of matching "we" (pidämme)?

Because the subject is in the genitive (meidän), it doesn't trigger the normal verb endings like -mme. In these necessity sentences, the obligation verb pitää is always frozen in the 3rd person singular form (the "he/she/it" form).

Does the second verb, tehdä, need to be conjugated to match "we"?

No, tehdä (to make / to do) stays in its basic dictionary form, also called the 1st infinitive. Obligation verbs like pitää are followed directly by this basic form, similar to English: "must make".

Why doesn't the object budjetti have an -n ending?

Normally, a complete object takes the -n ending. However, there is a special exception for necessity sentences: because the subject (meidän) is already in a genitive-like form, the object drops its -n and stays in the basic nominative form (budjetti).