Converting metal building

I’m in need of some advice. We have a metal barn (2, actually, one with sides and one without, 30x30 and 30x40, both with running water, power and a concrete slab).

My wife works out of town and in lieu of packing up and moving, we’re interested in enclosing part of one of these buildings as a living space for a couple of nights a week if it’s cost effective. Oh, it’s on 50 acres that won’t be sold in our lifetimes. (Family land). After she retires in 5-6 years, we’d like to use it as an occasional weekend getaway type of place. I’m already retired.

I’m trying to get a handle of how much it would cost to enclose half? This is a cost issue so we’re not interested in special doors, windows, fixtures, etc. Inexpensive, basic, clean and we don’t have to do everything at once. Maybe have one bedroom and a den/kitchen plus a toilet and shower. Don’t really care if the walls are drywall or if we use something like bookcases for the walls. Also, since the ceiling is high, could we leave the roof exposed and have a loft for extra space? Ceiling is probably 12-14 feet high and its in central Mississippi where it’s hotter than hell, does get cold occasionally but never lasts longer than a couple of days. I just need some ballpark estimates because when I look online, most examples are situations where someone wants a space as nice as their home. Oh, I’ve also been looking into composting toilets because septic systems seem awfully expensive.