Ballast?
 

What are you using for ballast? How are you mounting it?

I need to add some weight before the next event. I don't have a welder, but I can bend stuff and drill holes.

Is something like this a fair deal?
http://mazdaracers.com/classifieds/item/1362-ballast-system/

$125 for the mount
$27.50 per 14.7lb plate
+shipping

That is a really nice way to do it. Every other way I've seen is less nice than that. I've seen people melt scrap lead into 5# or 10# bricks and bolt them to their floorboard, which is the most obvious place to put it thanks to the low CG and easy access in otherwise wasted space. But there might be more clever places to put it depending on your particular car's weight distribution needs if you really want to get complicated. But I would just do simple and easy, which the Mazdaracers box appears to be.