I think the first thing to decide is do you definetily want to go to a gp or spend 3 or 4 days riding around spectacular roads in the north of Spain.
Another option to going to Jerez is the catalunya gp on June 10th. We could go across from Bilbao travel across the top of spain through the pyreenes and drop down the costa brava coast to Barcelona. My spainish road atlas gives bilbao to barcelona as 614km ( Bilbao to jerez 994 km) a distance much more do able in a days riding plus we would be travelling through more suitable nsr territory. This option could give the best of both worlds. I think realisticly Jerez would be 2 days travelling without the ferry trip which i believe is about a 24 hour journey making it nearer a weeks trip but going to catalunya could be done in a long weekend making it more viable and giving the chance for more people to make the trip.
By the way max I will definetely sponsor you, I considered doing this myself but I would have probably ended up paying most of the cost myself.