N64 is starting to rise but it's not quite there yet, at least not over here. If it's anything like the SNES it might shoot up within the next couple of years but thankfully for the time being it's still very affordable and a great system to collect for. I usually stick to loose carts and even on eBay you won't pay more than £10 maximum for most of the popular games. The less known/sought after stuff isn't even £5. There are still maybe only a dozen or so games with "silly" prices, and even games on the higher end of that scale like Conker really aren't all that bad when compared to what various SNES games fetch.
And yeah, Saturn collections are the path to madness. I acquired a tiny collection of fairly common PAL stuff about ten years ago when it was still cheap but lusted after a Japanese Saturn forever. Finally caved and bought one years ago and oh look, everything worth playing now costs almost as much as the console did.

Other than the stuff it came bundled with I've only bought two (cheap) games for it since. LESSON LEARNED.