Replacing galzanized plumbing?

[JT Spangler]

Got a 2/2 cottage under contract, and the inspector reports that the water pressure and drainage is not great because of the original galvanized pipes. This isn't a job I've tackled before, so my questions are:

(1) What's the difficulty level for me to repipe it (with PEX, maybe? And PVC drain lines)?

(2) What's an approximate price to hire it out, so I can ask for an allowance from the seller?