Hello and Thank you for choosing Just Answer.
The seal onyl costs about $30 and depending on how bad your ebrake shoes are, You may need to replace those also. On a difficulty scale from 1-10, I would give this a 5.
Below I have the procedure to replace the axle seal.
Note: You will need two special tools a seal remover and istaller. Both of the tools you should be able to rent from a local parts store.
I the axle housing vent is plugged with foreign material and causing the oil seal to leak, will clearing the vent solve the problem or will the seal still have to be replaced?