coming from someone whose family is in the dry cleaning business: it really depends. if the stain is really old and has been through multiple cleanings, it might not come out so easily. we used to have people bring in shirts that were really old and expected that we work some sort of miracle for $0.99 a shirt. you can always ask them if they scrub the collars (of course they might lie, since you'll never really know)
if it's just a few shirts and you don't mind the work, you can always make a paste w/ your detergent a a tiny bit of water and scrub the collars yourself. then take them to a cleaners to get them cleaned, pressed, and starched. you can probably find a place that's right around a buck a shirt and that's worth it just to get them pressed, imo. it might be $2.50 if they press the shirts by hand. most 99 cent shirt places will have a machine that can press shirts very quickly, thus the cheap price.