The common wisdom seems to be Invoice + markup of $500 to $1,000. This is true whether you do European Delivery or "normal" purchase. I've seen some posts where very good negotiators tied into a special promotion and have successfully negotiated below invoice.
It does seem that many people on the 'fest report the greatest satisfaction with their transaction (price, ease of completion, delivery process, etc) when using one of the board sponsors. I for one can attest to a smooth, thorough and fair transaction with Jon Shafer.
To give an absolute price would depend on the options you choose. I think you'll find that many 'festers special order their cars, again whether for ED or normal delivery. In the scheme of things a few extra weeks wait is a small inconvenience to have the exact car that you desire.
Remember that sales price is negotiated independently of rebates, incentives, financing, etc.
2010 535i: Deep Sea Blue | Natural Brown | ED: 6-Aug-2009 | 2013 535iX GT: Neptune Blue | Venetian Beige | ED: 31-Aug-2012