First, you should use food grade plastic, then there are lights, a pump, shelving, growing medium, fertilizer, ph adjustment, extension cords, timers, cups, air tubing, and air stone, and a bunch of other stuff.

Then you have to get it all home, double and triple check you are doing it correctly.

I don't think I spent $500, but no way anyone can put together an equivalent system for $25. Like most things, there's a lot more complexity than people realize.

Service, support, ease of use and setup, and, in the case of something that might be visible in a readily trafficked area, aesthetics.

If those things are not valuable to you (and they may not be) then you are not the target audience.