If the "cosmetic" problems include water stains or bubbling siding (delamination), those are generally quite good signs that there has been some water leakage and potentially structural damage or a lot of other headaches. Avoid such things if at all possible. With old enough units, it does get harder to avoid any tiny sign of water intrusion, and if quickly and properly repaired it can be only cosmetic; but very often it's a much bigger problem than appearances would at first suggest.
Alternator and battery (house or chassis or both?) are not huge problems in themselves, nor likely to be super expensive. I would be concerned with other things that may also need work. If the tires have not been replaced ever on your friend's unit, they also would need replacement for safety, and that does get expensive...a thousand dollars or more, depending on the chassis.
RV stoves are pretty much always gas cooktops, so running them off of solar power is not possible. An electric stove requires a very large battery bank (and solar installation) to do much with. An induction range is a bit more practical, but still needs a pretty substantial setup for much cooking. Running the TV and lights and maybe fridge off of solar power is not at all unreasonable, and with a sufficiently large battery bank doing some limited microwaving or running a coffee maker is practical as well.