A huge selection in this category awaits you. Of course, you have a budget ceiling and that is fine because there are still a number of quality guns to be had in this price range. If you're considering Glock, don't forget to checkout the Glock 19. A very popular sidearm and well worth your consideration. Then there is the standard Springfield Armory XD9 series which can be had for around $430 at gun shows (new in the box). A very nice piece is the Smith and Wesson M&P9 which will come in close to the top of your range. Excellent ergonomics with this gun. Ruger, Taurus, even Kel-Tec all have offerings for you to see.
Best thing is to go to a large gun show where you can see a wide variety of 9mm pistols, can handle them, and compare with the various offerings. Once you have managed to come up with a list or probables, try to find an indoor range where you can rent some of them to see how they feel and shoot.
Lastly, take your time and do your homework. Things such as complaints, problems, company support, etc. can be found on websites. It's good that you mentioned you were not in a rush. I would tell you this without reservation. If this gun is to serve as a self defense firearm, reliability should be at the top of the list. Stay clear of guns which seem to have a record of failures to fire, jamming, stovepipes, or anything else that could mean the difference of a BANG or a CLICK when you need it the most.