Paper accepted at a probably predatory conference, how shall I proceed?
Don't go.

You write that it's a valuable experience to attend a non-undergraduate conference, and it would indeed be the case, but you won't be attending anything like a non-undergraduate conference. Example story, and that actually reads like one of the "better" predatory conferences, since I've read about other predatory conferences where keynote speakers don't show up and attendees talk about completely unrelated stuff (e.g. a number theory talk at a food science conference).

This kind of event won't help your CV either, because if someone checks the conference out they'll discover that there's no quality control, meaning the quality of whatever you presented is now suspect.

Since you gain nothing by going, is there still worth going? Possibly, but any reason for going would be much less tied to the conference than to other things, e.g. perhaps you know someone who lives near the conference venue and have been looking for a reason to visit. If you don't have these reasons, you might as well save on the cost of travel.