Would you be happy with the STF-1? Probably. But, if I were you, I'd go with the STF-2 at a minimum. I don't know how much you are affected by the upgrading bug, but with the STF-1, you'd be buying HSU's lowest-end sub. I'd always wonder what I was missing if I went that route.

With the STF-2 or VTF-2, you'd get a 10" woofer and better performance. I presume the STF-3 and VTF-3 are out of the size/price range. If I were you, I'd go with the STF-2 at $399. As an aside, I own the SVS PB1-ISD like PMBuko, and I absolutely love it. But, it seems like it is also out of the size/price range you are looking for.