I wouldn't buy one. It looks set up to use a computer power supply, which are pretty awful. Most audio does not use switching power supplies because they're noisy beasts with lots of RFI thrown off. You could run it from a 12V wallwart, though, but a decent one would probably double the cost. You would probably want to case this and add knobs, jacks, a selector switch, and so on. To put it into decent shape, you'll probably fall into the $100-$200 range to complete it.
That's roughly the same as buying all the parts for a DIY preamp or headphone amp. Don't think you'll be saving much by not assembling the circuit. The most labor in DIY projects is found in casing.
If you're interested in a DIY tube preamp, stop by the DIY Forum. We'll link you to a bunch of designs and help you out.
