diapers are breaking the bank

Why do they have to be so expensive? With 2 kids in diapers we spend about $100 a month on diapers. I cant wait to get David out of them. Unfortunatly at 2 1/2 he doesnt seem to have to much interest in ditching the diapers. He will get really excited about the potty one day then will not want anything to do with it for a couple weeks. I know its not a huge deal until he is 4 then its considered a delay but my wallet cant handle this strain for too much longer. And dont get me started on the cost of wipes. Not when David keeps pulling them all out of the box and squeezing the liquid out all over the place. I am open to any tips you may have for potty training.