I've spent a lot of time in Japan and have been shopping FXs for people for years. Here's my take:
1. Zenki $200-$300
2. Zeroigar $150-$200
3. Chip Chan Kick! $120-$200
4. Nirgends $60-$90
and then...
Dragon Knight IV- I hope that no one here has spent a lot of money on it. It is a very cool game but over the last few years I have not seen it -in stores in Japan- used in mint condition for more than $50. I do remember it being hard to find at one point and getting quite a high price on ebay but $120 is extreme. On Yahoo auctions in Japan, there were a couple of sellers pushing it for $80+ but there were no takers afaik. In fact, it was the same two sellers who kept reposting it as they had no takers. That being said, I would still pay $50 for it if I needed it but anything much over that is unnecessary.
The Anime Freak 4-6 titles are a little tough to come by at all anymore but, again, never more than $40 a piece- and usually less. The Tengai Makyou Kabuki (name escapes me at the moment) game can also hit $40.
As for Super Real Mahjong FX- again, I don't recall it being difficult to find or expensive. It's been a long time since I looked for it though but I visit Japan again this summer, I'll be sure to keep my eyes open for updated prices.
All in all though, FX prices are reasonable except for the big three and even then it's because those games jsut stay in people's collections. In my almost four years in Tokyo, I probably saw each of the big three two or three times each on a shelf.