Is it permissible to recite istigfar and dua of prophet yunus with the aim of getting billions of halal money to spend it for Allah'sake but the main goal of reciting the dua is to please Allah or it is shirk?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Tawassul (to plea Allah by virtue of good deeds) is permissible as Allah Says (what means): {Those who say, "Our Lord, indeed we have believed, so forgive us our sins and protect us from the punishment of the Fire."} [Quran 3:16]

This is also proven by the Hadeeth about the three persons who were blocked in a cave and they supplicated Allah by virtue of their good deeds, and Allah subsequently made a way out for them.

Istighfaar (seeking forgiveness) and reciting the supplication of Yoonus are among the good deeds that are permissible to seek intercession by virtue of. Allah has promised to increase the livelihood of those who seek His forgiveness. Allah Says (what means): {And O my people, ask forgiveness of your Lord and then repent to Him. He will send [rain from] the sky upon you in showers and increase you in strength [added] to your strength.} [Quran 11:52]

There are many texts in this context. Therefore, there is no harm if someone seeks the forgiveness of Allah with the intention to increase his livelihood, provided that he does so with the intention of seeking the pleasure of Allah in principle; and this should be the case of a Muslim.

If he wants with this provision to obey Allah and spend it in His Cause, then he will be rewarded for his good intention, Allah willing.

Allah knows best.