I spent the afternoon setting this up. For $400 I got the hack squat/leg press with 4x45lbs olympic plates. I'm wimpy enough that will be enough to start, but I remember using as much as 6 plates per side about 8 years ago.

i'm kinda disappointed that I wont be building one, but the practicallity of buying one has worked out for me. Who knows, maybe someone will find this thread and get some ideas from it.