When completed, recycle and look in a charity shop for a new one. I'd picked up bargains. Bought two less than £2, unused. Recomend to look in charity shop and The Works.
Finding puzzle books are expensive now. I save my rewards for the coop.
Every Saturday the i weekend paper has a good selection of puzzles.
Oh and I like jigsaw puzzles too - but only 500 pieces. I look for those in charity shops but almost every time there is at least one piece missing. Not like I can expect the charity shop staff to do every puzzle that comes in to check it LOL.