It's about $22 a sample. They send you a free kit in the mail (couple bottles, zip lock, etc. for a secure mailing), and you send them a small sample of the oil. You can see on Jeff's report that they have national benchmarks for your engine that they compare against, plus they'll comment on anything else you ask about or they observe (such as the TBN).
I think your first submission is good for checking you against the overall benchmarks, but from then on out each additional submission gives you numbers to trend against the baseline you set on your own rig. So you can see trends or problem areas that appear over time specific to your rig.
I don't send mine in on every oil change, but I check in every 15k or so to see how things look.
1976 FJ40 - green and mostly stock
1996 FZJ80 - not so stock