OPGI is the LAST place I'll ever buy anything from.
Year One is expensive.
"I" would buy brand-name, top-quality ball joints from either a local supplier; or a place like Summit/Jegs. I'd get the polyurethane bushings from Summit/Jegs, too.
Other folks will remind you that there are sponsors of this web site that sell chassis parts.
Main issue: Don't buy cheap-junk ball joints imported from the Third World.