ThatGuyAroundTheCorner :
Well DSzymborski
Do you have any opinions on compatible Motherboards for my CPU (Intel Pentium G3258 3.2GHz Dual-Core Processor)
The one I posted is a good budget board and supports an G3258 in all BIOS versions.
Even if you don't choose one, I recommend going intel with the pentium here - it leaves you the option to put in an i3/i5/i7 as you desire when your budget allows it.
If you start with a 6300, while you can theoretically upgrade to the 8350, the 125W CPUs do not do well on the budget motherboards of the type you'd be looking for with your 6300 at this budget level.
Whether you go with a budget EVGA/Corsair/Antec here, I'd definitely look to upgrade it in a few years to a more robust PSU. At a $400 budget, you're looking at fairly entry-level PSUs (though I big step up from the junk out there).
If you're looking at $500 instead of $400, that changes a number of things - I'd look to get an i3 and a slightly better PSU at least.