I always tell people to figure $20-$40/gallon for a reef tank. Going used, you might get to $10/gal.
I've had a mixed bag with used pumps, so if you are like me and budget conscience, I'd just go with Jebao pumps and wave makers. That is what I use with no regrets.
The pump that came with my tank just died, I ordered 2 DCW-6000's to use. (1 for return, one for backup).
I also run 2 SCP-150/180 (can't remember) gyres and a SOW-8 wave maker for in take movement.
So far no complaints, and I've been running them since ~April, 2020 when I adopted this tank!
Tank is a ~20 year old 92 Corner. I'm moving to a 120, and the equipment will move with me. For me, it is very hard to spend the money on the big name products that are $300-500 min per item when I can buy an equivalent pump w/o the bells and whistles for $100.
HTH,
-Chris