if you intend to repair the crack for aesthetic purposes, don't waste your money.
a touch up will always look like a touch up, and chances are that it would actually look worse after the touch up (especially if its a shit job).
unless you are certain that the crack is so deep that it would actually cause the wood to be damaged due to exposure (a proper luthier will know), then you can repair it.
the only way to fully restore a crack would be to refinish the guitar, which would cost at least $200