[T]he old SNES cartridge probably costs upwards of $100 now.
NES ones a decade ago were like that, too. Rescue Rangers 2 and Final Fantasy were in the Kay Bee cutout bin when I got them and I ended up selling them for about $100 combined. Super-rare games like Dragon Warrior IV (really any Dragon Warrior game past the first; they didn't make many of them before Enix America folded) went for a whole lot of money, too, especially if you still had the map that came with it (it ripped easily, as did the booklets to FF1 and FF6/3, which had a mini-walkthrough of the first quests. I had those booklets but the covers came off).
I sold Fripp & Eno's Evening Star on Amazon for $50 back when it was OOP.
The outrageous cost of retro cartridges is why I haven't bought one of those semi-legal consoles that accept NES, SNES, and Genesis games (I think some models had Game Boy as well). Emulation is easier; you can get the games (a) for free and (b) without having to search all over creation to find. I guess these official NES/SNES mini-consoles are the equivalent of a Crosley turntable (only it doesn't destroy your records).
I bought FF7 before I had a Playstation. I was saving up for one when I found the game used in a video-game store for half the price of new so I struck while that iron was hot. I eventually got a scratch on the first disc that I couldn't polish out with toothpaste so I couldn't start a new game.
In a dungeon in the first Final Fantasy is an area where you have to fight giants -- a hard monster -- literally every step or two. You don't actually have to go in that section; it's just for the sake of a few treasure chests (I don't remember if they were worth your while or not).