I would suggest that you wait until you actually attend the academy. For starters, they'll probably provide handguns for you to train with if you don't own your own. Plus, as a cadet, you may be able to purchase your firearm through them at a reduced price.
When I became an officer (long enough ago that I'm retired now) our department carried officer owned guns. Without getting into brands, I found that with certification that I was a police officer, I could purchase either of the two approved brands from the manufacturers for a fixed price that was considerably lower than dealer cost! That even included delivery through a dealer who normally stocked the product line.
BTW, since Glocks have been mentioned, they probably have the most aggressive police purchase program around. The last price I saw on them (about three months ago) was right at $300 new. That's about 2 bills cheaper than a good retail price from a dealer. So if you're close to going to an academy soon you might want to hold off for a little bit and see if you can save some money.
And for everyone out there wondering how to participate in the program, you can't! If you can, somebody in the agency you work for has probably already told you about it. To the best of my knowledge, none of the companies even offer their programs to retired officers.
The only reason I even know anything about the Glock program is that a childhood friend of mine administers the program for Glock in a large part of the United States. And even though I could tell you when, where and with whom he lost his virginity, I still can't participate in the program. (Maybe if I offered to share that last bit of information with his wife...
But I doubt it!)