Memory prices doesn't really matter. You have to have more than 4GB even if it would be expensive. Too much of the first 4GB gets consumed just to have the desktop and a web browser open.

The main driving force for 64-bit processors was the database industry, since they need to handle more than 4GB of data and wants one integer to be able to store the address information. And with a 64-bit processor, they can also memory-map terabyte-sized databases, letting the virtual memory system map from disk files into RAM.

For "normal" use, photography is probably one of the few areas where 64-bit processors gives a big gain. Focus stacking, panorama stitching etc consumes huge amounts of memory. For most other applications, a 32-bit processor would work well if Windows just leavs enough memory to the application.