The cost of getting a coin graded, adding in shipping both ways and insurance, is going to run you between $30 and $50. The variance is largely dependent on how many coins you are having graded, since shipping and insurance are pretty much the same for one coin or 10.
(That's why many people will save up coins to be graded until they have a sizable batch).
So knowing the cost of grading, you should then compare that to the value of the coin, post grading. If you're going to spend $30 to establish the coin is worth $25, that might not be a wise investment.
Some will set a $$ amount on value before grading such as $100 or $150, which seems a little arbitrary to me. There are lots of reason to have a coin graded and not all of them are economic, but being able to do a basic cost/benefit analysis should help with decision making process.