We're looking into buying a home right now and have been looking into this stuff recently. The short answer is that the amount that you will need for a down payment and mortgage payment will vary widely based on your credit, the price of your home and the interest rate you can get on a loan.
For most loans, you'll need at least 5% down. If you put less than 20% down you will have to pay private mortage insurance, which is paid monthly as part of your mortgage payment and can vary from $50 or so to $100 or more. You continue to pay this until you have paid off 20% of the value of the house, you have paid your mortgage on time for 5 years, or the value of the house has appreciated so that you have enough equity in the home. 20% is a great goal if that is at all feasible.
The mortgage payment is going to vary depending on the interest rate you get, which is going to be based on your credit score, and of course it depends heavily on the price of the house and the term of the loan. You'll pay more interest over the life of a 30 or 40 year loan but have smaller monthly payments than you would with a 15 or 20 year loan. If you can make it work, you'll save 10s of thousands of dollars with a shorter term loan. Another thing to consider are property taxes and home insurance. Typically, you pay 1/12 of the yearly amount with your mortgage payment each month and the money is held in escrow so that you don't have to come up with however much that amount is at once. That will vary from area to area - we're in FL and have fairly high taxes and insurance, and some states have higher costs and some lower. There are some good mortgage calculators on the web.
Here is a good one. You can change the amount of the loan, the term and the interest rate and see how the payment changes. Just for example, for a 30 year, $100,000 loan at 6.25% interest rate, the monthly payment (principle + interest) would be $615.72. You would add the 1/12 of the yearly taxes and insurance - for me this would be about $250, and I would end up with a payment of about $865. If you've put less than 20% down, tack on another $100 for mortgage insurance. The taxes and property insurance may be more or less in your area - honestly, they will probably be less. Florida is notoriously expensive, especially as far as insurance goes. That was the part that really surprised me when we first started to look. At first glance, it seemed like our mortgage payment would be about the same as we had been paying for rent, but in reality, it will be that $250 more.
I hope that was somewhat helpful. There's so much to think about and consider, and I still feel half lost myself. It took me a couple of weeks of reading articles, discussing them with DH and pestering MIL, who is a realtor, with questions to feel like I had any grasp at all on it. Good luck!
Mortgage companies, IMHO, tend to overestimate what one can afford. You get into a house and then you have no money to do anything else!) Also, to reiterate what the PP said, in some parts of the country, it is actually cheaper to rent. Good luck!
