The last of AMD's 90nm parts will be hitting the shelves soon. The Athlon 64 X2 6000+ and the single core 4000+ are expected within the next few months, a slight revision from their original plan. The 6000+, with a 90nm process and operating at 3.0GHz, will consume 89W of power and will likely be the most power hungry X2 we'll ever see.
The FX line isn't receiving a last 90nm upgrade, but instead is being delayed until 65nm is ready to roll. Pricing on the last 90nm parts isn't made available, but if you are wanting to grab an X2 it is probably best to just wait for 65nm or stick to an older part.