Worth building?

I don't know if this idea is plausible, or even affordable...

I have an unused Intel i5 3570k processor, after upgrading due to a faulty motherboard prior, and I've been really wanting to get an "on demand" type of environment going. I've considered buying a Raspberry Pi or equivalent... but having the unused processor seems like it would be the most beneficial.

What I would like feature-wise: WiFi (I have an 802.11ac router), 8GB ram or more, HDMI output, and USB 3.0.

I do not plan on getting a GPU, as I do not see a need for it, as it will not be used as a gaming computer; however, having the ability to upgrade it later would be nice. I am curious if monitors can function similar to TV's with dual input, such as two computers one display via HDMI and DVI using source to swap between them. If so, that would be my primary display method, if not, I would connect via shell or VNC or just use one of my extra displays.

Uses: Programming/development environment, Virtual Machines (VNC server?), personal web/file/media server, and IRC.

MicroCenter? Yes, 20 minutes away.

Budget? Trying to stay under $250.

Parts needed: PSU, Mobo, Case, Memory, CPU Cooler

Parts have: Intel i5 3570k (CPU), 500GB 7200 RPM 2.5" (HDD)

Overclocking? Probably not.

Believe it or not, i think you may be able to pull this one off.

You will be stuck with 8GB ram and an H/B75 non-overclocking board, but in the end you're running a 3570k and she's still a snappy little piece of silicon. The board has HDMI out and a couple USB3.0 ports. Your WiFi requirement was a bit unclear (do you have a WiFi adapter already?) as you didn't list an adapter on the Parts Needed line.

Anyhow, here's what i came up with:
PSU: Antec VP-450w ($39.99) - $10 MIR = $29.99
Mobo: Gigabyte GA-B75M-D3H = $79.99 (Note that you can get a full-fat Z77 overclocking board like this MSI Z77A-G43 for ~$80 shipped on Ebay)
Case: NZXT Source 210 = $39.99
Memory: G.Skill Ripjaws 8GB (2x4GB) DDR3 1600 = $72.99
CPU Cooler: Cooler Master Hyper 212 Evo = $34.99

Grand Total: $257.95 w/o shipping, so figure something like $270-280 all-in.

Now, before you go off and buy all these parts BNIB, i would hunt around in the FS/FT subforum if you're warm toward used parts. I would encourage this, and you may be able to knock at least 25% off the cost of this build. Lots of excellent sellers selling quality stuff there.

Looks like a great list, and I will certainly be harvesting from the FS/FT board. Thank you =)

No problem

Grab an SSD when you can get some more $$$ saved up!