just get the bosch bov unless you plan un running 15+ lbs boost in anytime in the near future.... all the other BOV's run more than 3x the value of a used bosch which can be found somewhat easily on forums...
altho the HKS SSBOV sounds best in my opinion.. if you're only planning on running stock boost there isnt much need for it. but it is progressive, so if you decide to turn up the boost down the road it will hold fine there, too.. ive run over 20psi on mine and it sounds crazy loud letting out all that air
owell check supraforums.com for sale section, maybe you can find something used and cheap