This thread is quite entertaining, particularly the posters who are singing the praises of Preston with such determined gusto. And then the posters who think Preston is Lancashire's answer to Guernica. As always in cases like this, the truth is somewhere in the middle.
I've never come across Preston being compared to Edinburgh before. There may be a reason for that. 
. Someone said apples and oranges but I don't think you're even comparing two fruits. Apples and broccoli perhaps.
I grew up near Preston. I moved away when I went to university and never moved back although all my family are still in Lancs. What always strikes me when I'm back visiting is the single-minded belief that the locals have that their village, town, local restaurant, shop, etc is a-maz-ing. You're seeing this now with some posts on this thread.
The challenge comes that when you've lived in a big city you tend to be a little harder to impress. Because you've been spoiled for choice in the city. There are pockets of excellence in central Lancs. In particular I lament the sad demise of my favourite chip shop in Blackburn who did the best ever fish, chips and gravy. 
But I find that a lot of things people rave about turn out to be average or (sadly) disappointing. I know I've been spoiled. I'm wondering if this is the same for you too OP? You love Edinburgh. You're contemplating leaving because of property prices and work politics rather than because you've fallen out of love with Edinburgh. Do you really think you could be happy in Preston? You can't move and just replicate your Edinburgh life (which is what it sounds like you want to do). They're very different places.
Coming from Edinburgh, you won't find the Preston weather too traumatic. To be honest, I find Edinburgh grey and depressing (I think it's all that granite) but Preston is just mild and damp. I liked the comment someone made about anoraks. It always makes me laugh when I'm on a train from London going to visit clients in Yorkshire and as we get to the Midlands, everyone who gets on the train after that has an anorak. And sensible boots. When I go back home to visit, the dampness is what strikes me first. Especially in autumn/winter/spring. The penny drops that I am totally inappropriately dressed and I look out of place (even though I had thought about what to wear before leaving home!). I just always forget how wet it is. Of course that's why the countryside is so beautiful and green, and I still always have a little cry when I say goodbye again to those green hills.
I think you need to give some serious thought to your reasons for moving. You will need to start a new life in Preston rather than replicate your old one. Are you willing to do that? Will you regret it for the sake of £20k?
Finally, I agree with the majority saying don't live in Preston centre. You'll be disappointed. People saying "oh but Winckley Square's lovely". It's ONE square. It's been considered the nice bit of Preston for decades. But it's just one small square. I used to walk to work through Winckley Square every morning. It's nothing special. At all. Although compared to some parts of Preston I can understand why some people seem to think it's the equivalent of Heriot Row. Don't fall for that one OP. I think Lancaster would suit you better. Or if you want city centre living, maybe even consider commuting from Manchester. Still cheaper than Edinburgh and you'd be going against the 'popular' direction during rush hour. If you take the job, maybe rent for a while in Manchester while you get more familiar with Preston and central Lancs.