Don't look at the uniques - look at page views
The p4 2.4 or 2.8 with 2GB RAM will be fine for about 3 million page views/day (average cost will be 100-130$ with cPanel)
but you will be still looking at serious bandwidth though
and using CGI proxy will make you need more CPU and much much Less bandwidth
Consider multiple configurations and see what works the best for you
If 320$ are high - get dual core processor with 3TB - it will cost 200$ max (65% of your current offer)
