Well there are many fools that will slap in the biggest cam they can find and wonder why their vehicle isn't much quicker. Your best bet is to do the heads first, then have a cam ground to match them.

I wouldn't go to larger valves, they're plenty large for the bore you have currently. Anything more you'll start to hurt port velocity and lose torque.

$400-600 is reasonable to have them cleaned up using stock hardware. Then just budget your springs, retainers, and such.