There are stand alone TBC gears, but I suspect prices are still high, even as second hand; the DVD recorder passthrough is a cheap, yet valid, alternative; even one with a broken mechanic could be used, and you could have for near nothing…
I don’t know well the Diamond card, so I can’t say it’s good or not; I made my homeworks at the time, and the two ones I mentioned are amongst the best-for-the-bucks IMHO.
Take a look at these articles I wrote in my blog, maybe you could find some useful info there:
http://blog.sporv.com/high-end-video-capture-cards
http://blog.sporv.com/high-end-audio-capture-cards
http://blog.sporv.com/how-to-improve-video-capture-quality
Not aware of a professional transfer services, luckily, I always provided by myself, improving the quality of the captures during the years, thanks to experience, a lot of info found on the web, and better equipments.