I did the SAS (Saturday Arvo Sprints) series last year and am doing it again this year plus lakeside. They are great fun, all the info can be found on the QR website but to answer your questions. Price for SAS is $119 pre pay or $149 on the day, Lakeside is more expensive $189 or $219 on the day. These are just for street cars although there are some very serious 'street' cars out there. Class as divided in to cylinder groups 4, 6 and 8 and forced induction moves you up to the next class. There are other ones like WAS and Top Gear Sprints but I've never been so your best to look them up.
The next SAS is April 4 and there is a Lakeside open sprint on April 5. Will be a great weekend.