If you don't want to pay $100 for a gym membership, what sites are worth subscribing to (paying) for workout videos?

I have my favorite free sites, but I'm willing to spend $15 a month to follow an online fitness trainer. Presently, I'm looking at Sam Skelton on Grokker, because he has a core fitness routine that looks promising. I have lower back issues, and he incorporates all the same exercises that my physical therapists and chiropractors taught me--dead bug, bridge, plank, stability ball, weighted.