Душит жаба – what’s that supposed to mean?

There is an idiom "душит жаба" ("a toad is strangling smb") used when one wants to buy something but cannot force oneself to part with the money.

"Жаба душит" - "being strangled by toad", originates from assumption that heart diseases were caused by toads entering into organism with water, means "I get heartbroken by thinking about spending money".

Nobody really knows where the phrase came from but the meaning suggested above is correct.