Here we are at our next major stop along Chuo doori - the all powerful Sofmap. Sofmap actually has about five thousand stores in Akiba selling every computer-related thing imaginable. The one we're interested in is Store 13, right across the street from MediaLand.
Now before you go to me, |tsr, and say "Good Lord, why are you telling little children where adult Windows software is?!", you should note that these all are the stupid Knights of Xentar-style of anime pr0n games that are not going to "excite" anyone. So don't worry, parents!
Sofmap 13 is pretty well-known among collectors for liking to put software into horrible overpriced "sets" - the complete works of Namco on Famicom; the complete works of Square or Nintendo; all the Famicom gun games, and most recently all the Hacker International games (about 10 for 48,000 yen). The biggest set of all is near the elevator: in a glass case is contained basically every single piece of Famicom merchandise that is even slightly uncommon. All the limited edition games, all the accessories, all of Nintendo's original lineup, and so on and so on and so on - for around 600,000 yen. That's not going anywhere for a while.
Once you get beyond that, however, prices aren't that bad. Games that aren't in a glass case somewhere are usually below 1000 yen and the wagon of loose and box-free games always has at least somewhat interesting stuff in it. (This is a good place, by the way, to stock up on 100-yen Famicom baseball games if you want to beef up the quantity of your collection.) There's a stand with a fair amount of both loose and complete Disk System software, but nothing is below 1000 yen here.
When you get down to it, Famicom collecting isn't that expensive. There are a handful of games that get goofy prices, another handful of games that are a wee bit expensive, and then about 1000 games that can go for 300 yen on up in game shops like this one. Scanning Sofmap's list of prices they will give for certain games can be amusing, though - the gold-cart Punch-Out for 15,000; Ice Climber for 4000, the cartridge rerelease of Castlevania for 3500, etc.
Although I'm sure Sofmap doesn't want you to know, right next door is a small shop, Maruzen Musen, that has its own fair selection of Fami titles (as well as the obligatory 100-yen baseball bin). Maruzen also has the lowest prices in Akiba for AV Famicoms - 4800 yen plus AC adapter.