Difficult yes,because you have strip the gun to smallest bits and there is lots of painting involved (primer,under coat,hydro-dipping,clear coat...etc)... expensive... yes and no...if you have proper space,water tanks/tank,equipment then no but if you don't then yes...
The Sig looks much better in person but it doesn't look as good as Galil that's right,there is almost endless possibilities colours and patterns...