Pony up to the bar

This is a mash up of “pony up” (to pay money) and “belly up to the bar” (approach the bar).  The confusion might also involve the phrase “belly up” (go broke) as it also involves the word “up”.  Finally, the speaker might be thinking of those “animal goes into the bar” jokes.  For example –

A seal walks into a bar.  The bartender asks, “What’ll you have?”  The seal replies, “Anything but Canadian Club.”

Or maybe this is the one that the speaker was thinking about – A horse goes into a bar.  Bartender says, “Why the long face?”