You're best off buying your own guard roller. You can roll and flare your guards with the one tool. Like Craved said, most people charge about $50 per guard, but as far as I know, that's only to roll your guards not flare them. To flare, people charge about $65+. You can pick up guard rollers for ~$250, do your car and then flare 3 other people's cars and you've got your money back.
To minimize cracking and buckling, try flaring your guards on a really hot day so that your whole panel is nice and hot.