Use 'shell out' when you feel forced to spend money, especially in large amounts that you find unreasonable. After the flood, we had to shell out a lot for home repairs.
Pro Tip 2/3
Casual Context
'Shell out' is typically used in informal conversations, not in formal writing or speeches. I can't believe I shelled out fifty bucks to see that awful movie.
Pro Tip 3/3
Economic Discomfort
The phrase often implies slight distress or complaint about the amount of money spent. Fans are willing to shell out big cash for concert tickets, even if it hurts their budget.