How good is the International Journal of Pure and Applied Mathematics? (http://www.ijpam.eu/) I had recently submitted my paper to this journal on the advise of my guide and quite fortunately, I received an email a few days back saying that the paper had been accepted for publication. So before I pay the requisite fee of $165 (what is your opinion? is this too much?) I just wanted to know how good the journal was (the website says it has an impact factor of 2.13) and how much value such a publication will have. Would be really nice if someone could guide me on this. (This would be my first publication and I'm an undergraduate student)
This is the journal's website link: https://ijpam.eu/
To try to make this answer generalizable, here's how one can investigate in general:

The first thing to do is to ask more experienced researchers for their opinions, which is exactly what you've done here.  But you may run into the problem that you can't find people who know the journal.  For example, I don't recall having heard of IJPAM before, but it's not clear what that means.  IJPAM is certainly not a famous or prestigious journal, but there are a lot of journals out there and nobody has heard of all of them.

Beall's list is a list of "potential, possible, or probable predatory scholarly open-access publishers."  The publisher of IJPAM (Academic Publications, Ltd.) appears on this list, which is a bad sign.  You have to decide how to interpret it - maybe Beall has made a mistake, or maybe your criteria are different from his - but it's an important sign that you should investigate further.

You can then take a look at the actual papers and see what you think of them (or ask faculty members at your university).  In the case of IJPAM, I found it quite worrisome.  I looked at the most recent issue and found several papers that don't look like research papers at all: Sudoko: the new smash hit puzzle game and Odd and even number cultures.  This suggests IJPAM will publish nearly anything.  If you've written a research paper, having it appear next to papers with no research content would look bad, so I recommend against publishing in IJPAM.