How can I cheaply replace or repair the DPF filter in my Mazda 6?

I own a 2008 Mazda 6 2.0-litre diesel with 77,000 miles. A little while ago a DPF warning light came on and the car went into 'limp' mode. I spoke with the Mazda dealer who suggested the DPF filter required replacement, along with other items that may or may need replacing, cost between £2,600 - £3,500. After talking to a few people the car went to an independent garage who said they could do it for a lot less. £700 later the filter apparently was replaced, but he could not get the car from limp mode - in other words nice try but no banana, and £700 down the pan. I then went back to Mazda for a vehicle diagnosis. They claimed the filter was 38 per cent blocked, well beyond regeneration, and the original quote stood. Please help in any way you can.

Asked on 28 May 2011 by MP, Wigan

Answered by Honest John
Happily, these people have a fix:

In years to come it may not be legal because the tax status of the car and its EU rating depends on it retaining its DPF, and this may later be tested for.
Similar questions
We have owned a 2007 Hyundai Santa Fe 2.2 CDI 7-seater for three years but recently it has displayed the engine management light. Our dealer carried out a diagnostic check and revealed it was a clogged...
I have been approached by a local Volvo dealer who is aware that I am in the market for a new car and of my concerns regarding the DPF. They have a special offer at present: V50 R-Design D2 (1.6) with...
The DPF light is showing on my 2008 Mazda 5 diesel. Some say it is the better option (and legal) is to remove the filter altogether. Any suggestions?
Related models
Neatly styled, entry-level models a good balance of ride and handling, excellent 2.2-litre diesel engine.

Value my car