Tune up is generally spark plugs, de-carb the engine, check timing and possibly even take carbs off and clean them and or replace the impeller on water pump.

An all of this you can do your self, with maybe the exception of cleaning the carbs, but it too can be done by you.

To have all this done your prob looking at 300-400 most of that labor will come in the carbs.

De-carb the engine is easy , go to a Johnson / Evinrude dealer, get tune up in a can follow directions.