That's not true. Religious priests, (i.e. members of a religious order like the Franciscans), take a vows of poverty, chastity, and obedience. Most priests are diocesan, (i.e. work for their territorial bishop), and take only a vow of obedience.
I'd imagine Osteen is like many non-mainline Protestant ministers, (especially on the prosperity side), and isn't at all shy about requesting copies of tax returns so that he gets his 10% tithe. Add book sales and other income streams and he is raking it in. The average Catholic family tithes about 1% of their gross income and diocesan priests top out under $100k including housing allowance. (That's for married priests with children, e.g. ex-Protestant ministers who converted and were ordained. Celibate clergy start out around $25k and live in rectories.) A very few Catholic priests, think Andrew Greeley, become rich on book sales or media appearances. Others skim off the top or have connections, (organized crime or otherwise), that bring in the bucks. But most of them do alright because they have decent healthcare, a pension, free housing, and no wives or kids.