I'd recommend a hks ssqv, I have one on my own car as I love the sound it makes. I wouldn't however be buying one off that seller, those ones he is selling are knock offs, the tell tale sign is the price, a genuine hks bov is much more expensive new.
If they are too expensive new buy a decent used one of one of the forums from a trusted member rather than a fake from some random on ebay as it will likely cause problems or break.
For more detailed info on how to spot a fake, here is a good link
bbs.scoobynet.com/scoobynet-general-1/92...pictorial-guide.html