In our house there's a worthless "sauna room" that the previous owners stored a hot tub in I believe. We're wanting to make it a laundry room and half bath but there's currently no water to the room. Any ballpark figures on what we can be expecting to run the plumbing for a half bath and laundry? It does not share a wall with a bathroom.

A lot of variables to this. 1 or 2 storey home? Are the supply pipes run in slab or in the attic. Does the room currently have a waste line in it (probably not)? Assuming it does not have a waste line in it, is there a waste line close by to tie into as well as the ability to vent it properly?

I believe this particular room was an addition at some point. It is off the dining room so the kitchen is the closest plumbing of any sort. It has a flat roof with no attic space. It does not have a waste line or plumbing of any kind to my knowledge.

If they had a hot tub in there, how'd they fill and drain it? Run a garden hose through a window to fill / let the room flood when they drain?

We were told they had a hot tub in there, I never actually witnessed it myself so your guess is as good as mine on the logistics of that operation.