Hmm, I'm not an expert, but I'd stay away from anything over 150 bucks, including parts and labor. Actually when I keep thinking about it, it should be less. You can buy both cab corners for about $40-45 for both. It shouldn't take a skilled welder long at all to weld them on. Not even 20 mins, I would think. So I'd stay away from anything over 100 bucks. If I were you I'd buy the parts yourself, and then get the lowest rate for someone to weld them on, if they want too much, screw 'em and move on!
$0.02