SoftUK are running the following promotion on their site between 20th – 23rd June 2008:

Project Gotham Racing 4 360 (PGR 4) for £10.99 when purchased when spending £4.99.  Also on offer during the same time period is Dead Or Alive 2 Extreme 360.

So for less than £16 (well £15.98 to be precise) you can get your hands on both games which is no doubt a decent offer.