"Cheapest i3 is 120 bucks."
Lol.
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel Core i3-4160 3.6GHz Dual-Core Processor ($108.95 @ SuperBiiz)
Total: $108.95
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-06-25 00:43 EDT-0400
i3 Also has hyper-threading, which gives it 4 threads, like the i5. Except the i3 has 2 threads per core and the i5 has 1 thread per core. So they both have 4 threads in total.
Meanwhile, the Pentium doesn't have hyper-threading. And overclocking the processor is time consuming, as you need to test it's stability overnight. The processor will also get more hot and it's life will shorten. Plus, it also voids your warranty.
The i3 already guarantees you have good speed and all, with the normal life expectancy. It's also better at multitasking.
And the cooler is 31 bucks including shipping. Hyper 212, I assume.