[Help] Performing VLookup in Google Script

Hello,

I'm working on a fairly complicated pricing calculator in google sheets, which I've been adding functionality to for months now, and a lot of my formulas are getting pretty heinous. I'm trying to recreate the logic in google scripts, with separate functions for different product categories, so that I don't have to navigate through a sea of cascading IF's every time I want to add or change something.

A problem I'm having to this end is that, depending on product type and criteria, I need to look up information from a variety of pretty large tabs of data. It's not entirely clear to me how best to perform the equivalent of a VLookup to this end. The results I'm seeing in google are more confusing than helpful.