Am I wrong for not wanting to pay?

So my family is throwing a small party for my grandma’s 90th bday. One of my cousin’s is coordinating it and she just told us how much we have to contribute. Grandchildren have to pay $250 and great grands have to pay $100. In my family, many of my cousins had young pregnancies, so the ages are a little .. mixed. I’m 24 and am a grandchild, but my cousins who are 26-30yrs old are great grandchildren, are only being asking to chip in $100. I’m honestly pissed because why am I expected to pay $250 when they’re OLDER and have jobs just like me but are paying way less?? My cousin (who’s coordinating) jokingly says “oh girl u can afford $550 haha” . Yeah haha my ass, don’t pocket watch. I pay over $1,200 in monthly bills and your son who is pushing 30 lives at home rent free with a JOB. Is he paying $250 also ? I also have two younger cousins who are 19yrs and are grandchildren. Are they expected to pay $250 each also? Like I can afford the $250 but it’s the principal. And then she didn’t even tell us what the money was going towards within the party.

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