Well, the first thing you should do is sign up on the Grand Banks owners forum Grand Banks Owner's Resources
and ask your question there. There are a lot of active participants on that forum including former boatyard owners and shipwrights who collectively know more about GBs than God.
If it's a woody there are about a zillion things to make sure a surveyor checks, and you need a surveyor who thoroughly understands wood boats.
If it's a fiberglass boat, the condition is a lot easier to judge, but you still want a surveyor to judge it. With a glass GB,the important things are the condition of the decks and subdeck, the window frames, tracks, seals, sills and glass. Also the condition of the exterior teak and, even more important, its bedding. Same thing with the butt, scarf, and lap joints in the cap and hand rails.
Look for signs of leaks in the overheads of all the cabins and in the tops of the recesses below the main deck, like where the berths are. If the flying bridge deck is leaking or the teak landing pad on the aft cabin top, this can admit water through the overhead because of the seams and plugs and the twenty million holes drilled into the subdecks for the screws that hold the teak planks down.
Major things to check with the teak decks are the integrity of the seams-- they should not be pulling away from either side of the grooves (this can be hard to see at a glance sometimes). Wet the decks down and see where the wet spots are as the deck dries out. Wet spots on one or both side of a seam indicate a separation.
Check the presence and condition of the deck plugs if the boat has a screwed-down deck (all but the newer GBs do). Missing or broken plugs can admit moisture under the planks, although it's not nearly as bad a problem as separating deck seams.
The other stuff--- engines, generator, electrical, fuel, fresh water, sanitation, propane, anchor windlass, and so on are pretty much the same as any other boat as they all use the same kinds of components.
GBs are not low-maintenance boats. Even the glass ones have a rainforest of wood on them, from the exterior teak trim to the construction of the bulkheads, cabin soles, doors, etc. I tend to think of a fiberglass GB as a wood boat with a fiberglass shell.
Our PNW boat is a fiberglass GB36 and we've had it for over 17 years so far. It's a lotta, lotta work to keep up with it. Ours is kept outside because we use the boat year round and going up to stay on a boat that's in a boathouse is not particularly appealing. If we kept it in a boathouse our cosmetic maintenance would be greatly reduced.
So if you want a low-maintenance boat, one that you can use-and-forget, a GB is not what you want.
Finally, unless you get amazingly lucky, $75 grand is going to get you a pretty crappy GB42, particularly in fiberglass. Not saying they're not out there, but it most certainly would not be a boat I'd want to mess with. If your budget was $150,000 to $300,000 I'd say you were in ballpark for a decent one if you were willing to settle for a pretty old one at the bottom of that price range.