What motherboard do you have?
Without changing your motherboard, your best bet is to buy a used E8700 and try to overclock a bit.
If you will change out your motherboard and ram, look for a lga1150 motherboard for about $50 and a G3258 cpu for $65.
Plan on overclocking the G3258 to the 4.0 level.
The nice thing about the G3258 option is that the motherboard will support a future i3, i5, i7 upgrade.
Your psu is fine for any cpu upgrade.