I used a set of the cantilevered bathroom scales to corner balance.....they are cheep, but even cheeper when borrowed from a buddy.
I did the job before the start of the season and finally got onto some electronic scales at an SCCA National Tour event in late August. The overall weight was damned close & the corner balance was still good.
I've seen these scales around for 2-300 bucks on evilbay....dunno who makes em', but there's no need to reinvent the wheel, I figure.