Is paying 350 Qatari Riyals for a comfortable family transport, instead of using a free bus full of laborers, considered an unjustified extravagance?

Extravagance and squandering are blameworthy in Islamic law, and what is required of a Muslim is moderation and temperance in their affairs. The limit of extravagance varies according to people's circumstances; what might be extravagance for one person might not be so for another. If the mentioned amount does not burden you and is not considered extravagance, especially if the rented transportation is more comfortable and suitable for you as a family, then one knows best their own situation and circumstances.