Welcome to the community, Guillaume!
I’d first suggest rethinking your base design because I can’t think of a reason why you’d have a separate table for product prices. So, you need 3 tables at most, as well as linked fields linking suppliers to products (I’m assuming not every supplier will stock something).
From there, use a lookup + formula or a single rollup field to figure out the lowest price of any given product (assuming that’s your criteria for the order).
This is a common sentiment expressed by newcomers to any low- or no-code platform, especially one as powerful as Airtable. So, you’re definitely not alone in thinking this but us, humans, have a tendency to overestimate our anecdotal experiences when it comes to making generalizations. In fact, we are pretty hopeless at inductive reasoning. Especially with already super abstract stuff like software.
My advice - fail, then report back.
Detailed questions explaining where you got stuck and how and why your base works the way it does tend to get resolved at a much higher rate because experienced users will immediately see fundamental mistakes with base design, formulae, and/or JS code. This, in turn, improves your odds of not just solving your current problem but getting a real eye-opener of a response. The kind resulting in an “aha, if I can do this, then I can also do that” kind of moment.
So, the nature of your questions should always be focused on the what (you’re trying to do), but the actual contents should be all about the how. Something along the lines of:
I wanted this...
So I did this...
Expecting this to happen...
But this happened instead...
Of course, this is all assuming that you want to get something done.
There’s nothing wrong with just wanting something to get done and not caring how that happens. There’s only so many hours in a day, after all, and learning about data structures, relational database design, and the like isn’t how most people would describe their ideal pastime.
But those kinds of questions tend to fall in the work-for-hire category - there’s even a separate forum for those right here on community.airtable.com.