Well, after my irritations with my xbox - I picked it up today from the repair shop.  I only had time to try one DVD in it so far - but I tried the most temperamental one - Gears of War 1 and it worked fine, first time.  It cost £60 inc Vat for parts and labour, it's a BenQ drive, I didn't want to flash it in my PC and whenever I've tried to solder electronics it hasn't turned out to be my 'finest hour' so I reckon £30 for the drive including some markup for the dude supplying it, and £30 labour - it would take me at least 2 hours and he'd got to have his markup - so it's fair enough. 
 
I just hope all the games work okay, and continue to work okay- hopefully for longer than the 2 years the last DVD Drive lasted.  I'm supposed to be getting a 250GB for Xmas, so once I've got that I might install everything to reduce the workload of the drive - see if it extends the life. 
 
If anyone is interested - the company is whitedog games, I think their site is www.whitedog.co.uk based in Stoke-on-Trent, just off the A500.