I about 95% sure that it's by rider. You do of course need to tech each bike, and if you're renting a garage at Thompson they charge by bike. At Palmer they rent by bay, and you can fit about four bikes in a garage bay.
Tony's a member here but doesn't visit regularly, so here's a mention: @
ttd
Or just go to the website and ask...
http://www.tonystrackdays.com