Unfortunately I don't have that much specific information, but my belief is that prices will be near current levels for the T60 since the CPU's themselves should be in wide availability by October. However this may be complicated by the fact that Lenovo will be releasing at least one new model (widescreen T-series) and I don't know if these will constitute T61's or some other new model type. With new models usually comes higher prices.
The prices on T60's now are awesome and Core 2 Duo mainly offers a performance boost, no battery life advantages, so personally I say go with Core Duo now if you can't wait. If I hear more details I'll let you know