I was searching for the best simulator programs for learning how to code PLCs.
Opinions are like noses; here is a look at my nose, YMMV:
IMNSHO, if that is all you are looking for
now, you can't beat RSLogix Micro Starter Lite. Smooth look-and-feel, ladder only, emulator free also. It's a bit daunting to get started, but videos abound on youtube e.g.
here. It's file- not tag-based, but that is an implementation detail that doesn't matter on a small project. No PID but that is trivial to code from scratch. If you get to the hardware stage, you can often find a MicroLogix 1100 on eBay for under 100-200USD.
Coding is the easy part; I/O and networking are much larger and more varied topics (check out the distribution of subjects for this forum). How exactly will it control the pump? Or maybe you are already familiar with that domain?
CCW has a free version with a emulator but it's like Fisher-Price. Okay otherwise; has multiple languages if ladder is not in your future; the first PID instruction is broken but usable, as is the second one written to replace it.
Siemens TIA has a trial version, but no simulator (I think?), and anyway it suffers from the "We are not intimidated by complexity, try to keep up" syndrome common a few time zones east of +0000.
A lot of the less common brands have free software with simulators, but they are generally at a "Hey, it works: ship it!" level of quality.