Mattyass: Your car sounds like its displaying the same symptoms mine had when I had issue with my MAF. Have you disconnected it yet and run it without? And if so, did it make a difference to your flat spot? Mine was undiagnosed for a while and I started losing noticable power at the top end as well. Car felt gutless...
Think I paid about £100 for a new Hitachi MAF on an exchange basis, but that was with a trade discount.