The on one inbred looks like it's on sale for 180 for the frame.
Since I'm a bike noob, what are all the parts I would need to finish this frame? Possible to be all in for 500 or under?
Doable, yes. Easy, no. First thing you need is a friend or a nearby co-op to help you through the build process. Second thing you need are tools, which said friend or co-op can often supply. Then, of course, you need all the parts:
wheels and tires/tubes
headset
fork
handlebar and grips
brakes, brake levers, and brake cables/lines (Inbred is disc only, either cable or hydro)
seatpost, seatpost clamp, and saddle
bottom bracket
crankset w chainring
pedals
chain
rear cog
some sort of spacer kit for the cog to get the chainline straight
maybe a tuggnut or chain tensioner of some kind (since Inbred has trackends)
I think the easiest/cheapest way to get all those parts is to get a doner bike and a singlespeed conversion kit. 26er hardtails are still pretty common lowend beginner bikes and are all over craigslist, e-bay, and discount websites like nashbar, performance, and bikedirect. You could probably find a suitable doner bike for a couple hundred bucks. It'll have lowend parts, but hey, you're trying to do this for under half a grand. Singlespeed kits are usually pretty cheap. In fact, On One sells one that you could order along with the frame. Basically, all that does is replace a normal cassette with a single cog and spacers. You might want to grab on On One rigid fork while your at it (I think they run about $80, but I've seen them on sale for $50) since your doner bike will probably have a crappy lowend suspension fork.
So, you buy a 26er, disc brake, donor bike. Strip all the parts. Chuck or sell the geared bits (and crummy fork). Reinstall everything else on the Inbred frame. That's what I would do in your shoes, anyway.