Make Alex spend his $$$ on this thing he invented

 100-199 members

Alex spends $50/day; everyone else spends $10 (or more, at their option)

— | | | | | —

 200-299 members

Alex $60; everyone else $10

— | | | | | —

 300-399 members

Alex $70; everyone else $10

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400-499 members

Alex $80; everyone else $10

— | | | | | —

 500-599 members

Alex $90; everyone else $10

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600+ members <——- WE ARE HERE RIGHT NOW

(Nice work, you bastards. $100/day. Top Ramen for me for dinner forever, it seems.)