It is open pretty much every weekend, there are only a few weekends when events take place and you can't go along, usually just the comp safari weekends. Even when booked by other groups, if you speak to the farmer you can normally get in.
?20 a car
We had a Disco 2 along on Saturday with road tyres, managed very well, even seen an L200 Mitsubishi go round on road tyres. Also get a few D3s along at times who manage ok.
Tow rope should just about do it, just go as part of a group.
Keep an eye on here (non SLROC Events section) , we normally post when going along, or stick a post up yourself and see if anyone wants to go.