I'm no expert, but to summarize what you should do:
-- First, determine whether your computer has a hard drive (like a desktop iMac or an older MacBook), or has a flash-drive-style data storage (like a new Air). If it has a hard drive, then STOP using the computer immediately, because everything you do causes data to be written to the hard drive, and you might be overwriting your old data. Turn off the computer and use a completely different computer to continue your search for answers. If instead your comouter has a flash drive, then it's not so much of a problem (unfortunately because the data is already unrecoverable).
-- Perhaps the only action you should do before turning off the computer is go to the "/Users" folder, and look for a file with a ".dmg" or ".sparsebundle" suffix that seems to have the same name as your lost User account. If you can find it, you might be in luck.
-- Contact any of the data-recovery firms mentioned above, or any other one near you, and tell them what happened, and ask for an estimate. If you can afford it and the price seems reasonable, hire them to try to recover the data. If they seem overpriced, try contacting a few others until you find a company you like.
-- Sometimes people have a "Time Machine" auto-backup happening to their home router, without them even realizing that this is occurring, because it is the default setting when you first plugged in your AirPort. This is unlikely, but it's a possibility, so (using a different computer) see if there is a hidden backup that you didn't even know about.
Good luck!