just found this site.
http://www.expertcar.net/index.php
In spanish but can be converted to English once you start the reservation process.
When you say the Tour do you mean France? If so you need to check the rules on cross border travel. Also when you say van, most vans will only seat 3. If planning to put 4 in a 3 seater I would keep that very quiet from them
4 seat vans may be harder to come across.
cost for next week for a Grupo 3 is 534€. Bookings not yet available for June 2011 which I also tried