Hmmm... I thought it was $20 for each cable for simple ones like throttle and clutch. Sorry if I led you wrong. I just checked their website, and you're right, it is actually $35 a cable.
Still, here's the thing. On my first attempt with them, they sent me a cable that was right, and one that was wrong. When I told them, the service was excellent, and they shipped me the right one (to Canada, no less) with no questions asked, and no problems. The cables are higher quality than I could have made myself (I tried, really I did.)
I'm no mechanical dummy, but I tried to make my own, and couldn't. Your results may vary, but for the price, Motion Pro really came through for me.