Despite understanding financial needs, I believe you need to upgrade on some parts. You get what you pay for.
You would need some type of IO thru a Display.
Note, faster ram won't do you any good if you don't get a processor that utiliizes the extra speed. Also, it will probably be cheaper to built with current day parts if your buying everything new.
Anyways, you will need a DC-DC power solution to replce the 150W PS or a Power Inverter in addition to your list. For proces/mothrboard, I would recommend you look into a Via ITX Sol'n. Highly practical for carpc usage.