well if I was going for a big cheap i3 - the adimlab gantry pro 3d.
https://www.amazon.com/ADIMLab-Assem...s%2C311&sr=8-5

It's the only one I know of that has all the critical prusa I3 design components.
1) direct drive extruder
2) bed side support rails
3) dual z-axis motors

Personally those are the main points I loook for in an i3.