。
I can't afford to pay that much money.
Literal
I [to-は] that-much money [object-を] pay-out leeway [topic-は] not-exist.
そんなに ('that much, to that extent') is an adverbial degree expression — distinct from そんな ('such, that kind of'). 余裕がない ('have no leeway') is the standard inability-due-to-resources pattern. The contrastive は after 余裕 emphasizes specifically the affordability leeway.