it would depend on your skill level & tools available
they are not really difficult to rebuild but can be frustrating to assemble you do need 2 types of snap ring pliers , pin type & flat ring type & you need some way to load the countershaft , , I bought the factory tool to do it , you can trim down an old counter shaft , I once managed to assemble a trans using heater hose just to see if it could be done
I guess i would say it is about 3 on the difficulty scale