I did that last April (2018). Had some friends "winterize" it for me and let's just say I think they at least accomplished finishing some beers. But anyway, I had busted galvanized pipe all over. I just started at one end and worked my way replacing it with pex (bought 100ft roll). Worked out really good and I put a couple drains off each of the main lines to make it easier to winterize from now on.

Big thing is buying the cheaper pex fittings (especially if you can borrow the tool). I used shark bites cause they are so easy but that is where the $ goes. Probably cost me $30 for the pex and $120ish in shark bite fittings. Could do it for 1/4 of that if you have the tool and buy the regular pex fittings.