I know this thread is well intended, but I totally, utterly hate price guides. If this thread was in Fighting Street I would drop some choice words.
1) Noobs get ripped off because they're impatient, impulsive, click-happy idiots, not because they were left to fend without a price guide.
2) Anyone who's been around six months already has a rough mental list.
3) Most of you guys in favor of making a list base too much of it on ebay prices, which are currently insane and can be found out anyway by looking at BIN items and completed auctions.
4) The list in turn legitimizes the prices asked by ebay parasites.
5) The list also becomes the new rock-bottom price, creating fewer good deals here on the forums and other non-ebay markets.
6) And yeah, it goes out of date real fast.
The problem with the Turbo is that a large number of games are very uncommon, especially when we get into CDs. When I was doing NES collecting before finishing my set, outside of NTSC Stadium Events, almost every US NES cart was available on ebay for example, at any given time. Games like Magical Chase, Tonma, Super Air Zonk, Bonk 3 CD, show up so infrequently that trying to establish any sort of baseline price for them becomes far more difficult than with other systems and price guides.
I still do see a legitimate reason for one, but the problem is that any baseline price we establish for a game will be in dispute from people who paid less or more than said guide value.
Added in edit: I'd like to have something as a reference for people who really want game X to know what a fair price is if they wait around, but the difficult part is establishing that price (let alone condition, with outer box, without outer box, with manual, with plastic tray if it's a TTI hucard game). It's helpful to someone who's had a Turbo lying around for 20 years and really wants to own game X but doesn't want to get ripped off for it.