Its funny what some people consider "low budget" most of us don't figure a $200 cpu as being low budget. I personally have never bought into the idea of future proofing, specially these days. New tech is developing fast, price are dropping faster and things are goings nuts. The best advice is find a good price point for what you want right now and build on that.
Posting your budget and what you plan to do with the pc will give people a better idea of what you might need.