Getting wildly different quotes to replace my HVAC. How do you know what’s actually fair?

I’ve been putting this off for a while, but I think my HVAC system is getting close to the point where it needs replacing. It still works, but it struggles during peak summer and it’s original to the house so I know it’s on borrowed time

I finally started getting quotes and the range has been all over the place
One company quoted around $8k, another closer to $14k and one was pushing $18k+ with upgrades I didn’t fully understand. All for what seems like a pretty standard single-family setup.

Now I’m stuck trying to figure out what’s actually reasonable vs what’s upselling

How can I sanity check pricing? Is it mostly about the equipment brand/SEER rating or does installation quality vary enough to justify those differences?

I don’t mind paying for quality, I just don’t want to overpay because I don’t know what I’m looking at