Switching steel for copper

What's a ballpark range for how much it would cost to replace some gavlanized steel piping with copper piping?

See below for details on the situation...

I live in Chicago, and my house is a cape cod that was built in 1949. Over the years, the handful of owners have replaced a good portion of the old galvanized steel piping with copper piping. What galvanized piping remains is 1) the supply to the house, 2) an elbow from the copper out on water heater to the rest of the copper hot water lines, and 3) the hot and cold lines running to the upstairs bathroom.

I fully understand that all of it will inevitably have to be replaced, but I need to phase in the work to make the financial strain easier to deal with.

The good news, according to the home inspector, is that all of the piping either goes straight up into the attic space where there is full access to all fixture connections, or straight down into the crawlspace (which is much deeper than any crawl space I've been in; you can actually stand up)...no destruction of drywall or tile necessary.

I couldn't begin to estimate that sight unseen. The price of copper these days will take your breath away, but there is also considerable labor involved in the tasks you describe.

Another option might be PEX tubing, but I know Chicago is sometimes fussy, and I don't know if PEX is being used there.