I've not seen this thread before so I'm glad P4UL B has reawakened it.
My biggest mistake was costing out the PPL and thinking I needed that amount of cash saved up before I could start the training. I had that belief because I thought I'd get the whole thing done in a couple of months. How wrong I was! When I discovered I was averaging about an hour a week I realised I could have started training much earlier and paid for it on a pay-as-you-go basis from earnings rather than from savings. Also, the cost of flying is only going to get more expensive so the sooner you start, the better.
On a practical level, find somewhere you can train that is cost effective for you and make sure you consider all the hidden costs like travel to and from the airfield, landing fees etc. Buy the training materials (books, whizzwheel etc) second hand from other people at your flying club or ebay. If you go out socialising and drinking then STOP! It's amazing how much you can save by staying in
Consider getting a second job if money is really tight. Lastly, consider different forms of flying as others have mentioned - microlights, gliders etc.
Good luck and let us know how you get on!