Hi Theresa,
Sometimes I wish I had a crystal ball so I knew exactly how much the ticket price increases would be!  Unfortunately there is know way of knowing when, if, and how much ticket prices will increase.  There are websites out there such as 
www.allearsnet.com that will give the historical data of price increases so you can use that information to try and forecast future...but still it's any ones best guess.
Personally, unless I were to catch wind of a huge increase, I would opt to keep my money in my own bank account until I absolutely had to turn it over to the mouse.  This would be especially practical if you are paying interest on a credit card, because the cost savings would be negated by the interest expense of the credit.
I would suggest signing up at a fan site such as 
www.mousesavers.com  or 
www.allearsnet.com to keep on top of the latest news regarding ticket pricing and discounts.  I have used 
www.undercovertourist.com to purchase discounted tickets.  It was a great transaction and they have wonderful customer service.
Hope this helps!