Because Betty's Worth It
In season 3 episode 20, the Black Hood and the Gargoyle King send a note to Betty (delivered through a chain of students at the school) in order to get her out of the Prom so that they could kill her.
In season 3 episode 21, Jughead is trying to track down who received the note directly from the Gargoyle King. He's on the 3rd person in the chain (Louie) and, before even asking Louie who he got the envelope from, offers Louie $20 for answering the question ("So here's the $20 question: Who'd you get envelope from?") Because Jughead knows that good, accurate information isn't free. And Betty's worth it, so he doesn't even risk getting wrong information by being cheap.
Now, after paying Louie, he's probably spent at least $60 (paying the jester, Luna the Druid, and Louie the centaur). Plus, he probably also spent some money asking around about who the jester was.
For a normal teenager, $60 is a bit expensive, but probably not a super big deal. But Jughead grew up poor, on the Southside. His family never had a lot of money growing up and, therefore, he's probably learned to save and scrimp his money and spend as little of it as he possibly can.
So, for him to give up at least $60, without being asked for it, without being told that he has to... How monumental is that for a poor kid who grew up on the Southside??? But he does it! Because Betty is important to him. Because Betty's worth it to him!