The Turbo-CD had a price drop from $400 to $350, first via a coupon rebate and then a new MSRP. Then the price dropped to $300. I'm not sure if there were any price drops between that point and the $150 drop right before the Duo. And I'm pretty sure the Turbo itself debuted around $200. I'd have to dig around for the receipt, but I remember the price being just under $200 at Wal-Mart when I bought mine (and Wal-Mart didn't really jack up prices any). The Genesis was the one that was $189-$190. The Turbo went $200 -> $150-160 (Bonk set) -> $130 (still Bonk set) -> $100 -> $70. The way the prices worked out you could essentially buy the the equivelent of the Duo (Turbo, CD, System Card 3.0 and games) separately for about the same price as the Duo.
I'm still skeptical about the Wii playing Turbo CDs. Would be awesome of course, but it doesn't make any business sense. I think Nintendo/Hudson would rather sell you a game again than let you play what you already have.