Well, the e8400 is priced $170.
If you want to go budget, the Phenom II X3 720 is the best choice as to price, cores, speed and overclockability.
If the budget is tight, the PII 545 is a good choice.
Then, if you are willing to pay $170 for a CPU, the Phenom II 945 is a great choice and, for the same money as the e8400, you get a QUAD core with respectable speeds and very good performance. Plus, in the future, newer games would run faster on the quad 945 than on the dual e8400.