I want to buy a dermaroller but all the listings I saw months ago on amazon are gone so now I'm kinda stuck. I see some people selling them for $6-7 on ebay, which are the purple color ones. I see some expensive zgts and dermacit ones for around $17-$20. Not sure what to do. The cheaper ones claim to be titanium needles but seems too good to be true. Any ideas? I'd prefer not to spend more than $20. Thanks.