Current prices for Yonah are still;
Core Duo
T2700 (2.33Ghz) $637
T2600 (2.16Ghz) $423
T2500 (2.00Ghz) $294
T2400 (1.83Ghz) $241
T2300 (1.66Ghz) $241
T2300E (1.66Ghz) $209
Core Solo
T1400 (1.83Ghz) $209
T1300 (1.66Ghz) $209
Rumoured prices for Merom (as no official pricing from Intel yet);
Core 2 Duo
T7600 (2.33Ghz, 4MB cache) $637
T7400 (2.16Ghz, 4MB cache) $423
T7200 (2.00Ghz, 4MB cache) $294
T5600 (1.83Ghz, 2MB cache) $241
T5500 (1.66Ghz, 2MB cache) $209
Current prices for Conroe;
Core 2 Duo
X6800 (2.93Ghz, 4MB cache) $999
E6700 (2.66Ghz, 4MB cache) $530
E6600 (2.40Ghz, 4MB cache) $316
E6400 (2.13Ghz, 2MB cache) $214
E6300 (1.83Ghz, 2MB cache) $183
Current prices for Woodcrest;
Core 2 Duo
5160 (3.00Ghz, 4MB cache) $851
5150 (2.66Ghz, 4MB cache) $651
5140 (2.33Ghz, 4MB cache) $455
5130 (2.00Ghz, 4MB cache) $316
5120 (1.83Ghz, 4MB cache) $256
5110 (1.66Ghz, 4MB cache) $209
In other words, there are no reason not to opt for Merom unless you factor in two things: 1) if you are Apple you probably get the current Yonah at a reduced price (think Mac Mini) and 2) availability.