@khashayar, I never compared Antec to SeaSonic (although Antec do have some quality PSUs).
The VP450 is a budget PSU, and would suit this build pretty well. Spending $50 on a SeaSonic PSU is usually a no-brainer, but in this instance, I'd look to the best quality to price ratio. Given this setup doesn't have a discreet GPU, and really isn't much of a power draw, either PSU I linked would be just fine.
As for upgrading a PC in a year, that's always a possibility....but I certainly wouldn't recommend building a ~$200ish setup with plans to upgrade, as that'll never work out well.
Again though; looking to the used or pre-built market is usually a much better idea when dealing with such a low budget.