This question is a litte vague, but I'm tackling as if you are a buyer comparing various homes.
Besides price, factors such as insurance and taxes (escrow requirements) will fluctuate. So while the actual mortgage payment on the home is constant these could change yearly and therefore change your expected payment.
Also, if you are not putting 20% or more down on a home you may be required to make private mortgage insurance payments. This generally decreases slightly as you pay down the mortgage and not all loan programs require this (i.e., VA, MassHousing) so this is a variable cost as well.
And lastly, rates change daily and the amount of points or fees charged by lenders differs resulting in different APRs. So, this could be a variable in the actual end result payment.
Price of Home
Interest rate on Mortgage / APR
Best of luck!