There is no way to tell. You should have asked his hourly rate or what the flat rate would be. If he was http://simplesitesbigprofits.com a flat rate plumber, he should have been able http://simplesitesbigprofits.com to tell you exactly what it was going to cost. If he works hourly, he should have been around $85-$125 like the previous poster said. He should have been able to give you an estimate on time.
If he works flat rate, or works based on the drain snaked, you cannot complain. This may very well be his charge (it obviously was). Hopefully he was a licensed plumber, and you got great service. You can always call a handyman, and not know if it was done properly.
Plumbers rates very greatly according to region. Even within regions, some plumbers are much more expensive than others. Some plumbers like to be paid a lot for a good quality job a few times a day, other plumbers like to do as many calls as they can in a day for very little money.