Ana: Not to knock Trulia (after all, they are putting up this site) but, nevertheless, Trulia is just a rough cut at things going on in the real estate world. First, you need to shop for a mortgage to figure out where you might get the best deal. After you align yourself with a mortgage company, they will be glad to start telling you of the expenses to purchase and monthly payment thereafter.
Next, you need to establish a relationship with a Realtor. That person will then give you up-to-date information on price and availability of houses in the areas where you want to look. The monthly tax burden can easily be calculated from information readily available to Realtors. It's a simple matter of dividing the annual taxes (honest to god, real taxes) by the number 12. The mortgage company will be able to give you a good faith estimate on your monthly principal.
There you go! All done (except for homeowner's insurance). Reasonably accurately, too. The closing expenses will also be estimated by several different entities. These are only so-so, in terms of accuracy, because expenses will keep coming in until closing day and earlier estimates may be off.
The whole process can best be understood by getting a Realtor to advise. All the stuff on the web is just fine but, as you have discovered, it can be far from reality.
Licensed in NJ and Pennsylvania.