If you get the 90bhp model it won't have a DPF. Nor will the 1.4 diesel, which is the more popular one to get.
Well looked after, a DPF could last in excess of 100,000 miles, but it all depends on where you drive, and how and where the previous owner has used it. I've seen some 2008 308s need attention to them as low as 60,000 miles.
One thing which isn't commonly known is that the EOLYS additive is squirted into the fuel system at every fill up. So if you or the previous owner have been putting in a tenner's worth of fuel frequently, it will empty the additive pouch in no time.
I've had many Pugs, two of which had the DPF, and they didn't have any problems at all. I only do a short motorway run daily to Elly Port. I didn't use any additive but always use Millers Diesel Ecomax in my diesels.
Its not as big a problem as some percieve. A new DPF is around £120 from CATS2U. You can buy the additive around £30 per litre and fill it yourself, then get someone like me with the Peugeot diagnostic equipment to tell the car's computer that it's been replaced and refilled. The only problem is replacing the glow plugs (they're used when regenerating). On some models they're round the back of the engine and a nightmare to get to. When I had my cars I got Chris Gilly and Benza to do the plug changes!
The biggest problem to concern yourself with is if the car has a dual mass flywheel. Replacing the clutch on one of those is shocking.
And another thing to watch for is servicing, and that the correct low ash oil has been used. I realise its anecdotal but the most problematic engine we see on the forums is the 110bhp 1.6 and problems are down to irregular service intervals and wrong oil used which causes oil starvation at the turbo.
The service interval is 20,000 miles and I personally think that's far too long a gap. Its all well and good for the manufacturer to state this, the problems occur long after the warranty and their liability has run out.
A friend of mine in Wigan has a petrol 207, and its pretty good on fuel, so don't dismiss them outright.
Hope that helps, give me a shout if you want to know anything more or have seen something already and want an expert eye cast over it.