spend good money after bad
Words that are commonly found together are called by linguists a collocation, from the Latin collocare to place together. So spending money is a collocation because those two words turn up frequently together for the obvious reason that ninety-nine times out of a hundred that is what we are doing with our money.
The expression send good money after bad dates back to the 1660s, so it has quite a track record in English. It has a more forceful variant, throw good money after bad, first recorded in 1690. The idea is that, having lost an initial outlay of money, it is hardly a good idea to spend more money on a worthless project in the hope of a happy outcome.
The current version of this expression which seems to be taking hold is SPEND good money after bad. Presumably the collocation spend money is uppermost in people’s minds and the rhyme send/spend facilitates the glide from one to the other. The only problem is that the syntax is now wrenched out of shape. We DO send or throw something after something else. We do NOT spend money after something. We spend money ON something.