Use this handy mortgage prequalification calculator to get a pretty good estimate of the property price you can afford based upon your income and debt profile.
Prequalifying for a mortgage is simple, and is intended to give you a working idea of how much mortgage you can borrow. Combined this amount with your downpayment, and you'll know the price range of houses you can afford. It is not the same as being preapproved for a loan, which involves placing an application and providing documentation to a lender.
Remember -- this is just a guide. Your final amount will vary depending on a number of factors, especially interest rate, which will be based on your credit score. When you're ready, a lender can give you a more exacting figure.
To produce estimates, both Annual Property Taxes and Insurance are expressed here as percentages. Generally speaking, and depending upon your location, they will generally range from about 0.5% to about 2.5% for Taxes, and 0.5% to 1% or so for Insurance.
Front End and Back End debt ratios are to determine how much of your monthly gross income can be used for your mortgage debt (front end) and how much can be used to satisfy all your regular obligations (back end). The 28% and 36% ratios are standard in the mortgage world, but lenders may have other combinations available, such as 33%/38%.