Like the others said, for a 10Km commute the optimum is a flat bar "fitness" bike. Light, fast, standard parts, with braze-on mountings for panniers and mudguards. I'd consider a drop bar roadie or touring bike if your route has no shelter from strong headwinds, but visibility from the roadie body position isn't great.
Bike brands sort of matter and sort of don't. They matter in as much as they are a marker of quality of design, parts choice and construction; for example "Huffy" versus "Giant" versus "Kona" versus "Bianchi". But they don't matter in that once you're at a particular level of quality, then there's not much to choose between brands (eg, they all use one of three brands of gear sets).
Bike years matter not at all. But retailers will insist on year models. So if you can, wait until they run out last year's model and leap upon that bargain. That's by far the best way to pick up a cheap new bike.
Bike features do count. The most vital of those is weight. Of the various techologies, get disk brakes if you can. For commuting you don't want shocks: because they add weight.
The way the bike fits and feels matters a lot. Because of that, do buy from a bike shop, do visit a lot of shops and test ride a few candidates before making your choice.
You are right to be worried about the all-in price. Here's a list of odds-and-sods, with some brands I'd recommend as being a good fit to commuting (ie, reliable without weighing a tonne):
- bidon cage, water bottle (2 x Elite Custom Race cage = $50, 2 x Camelback bottle = $10)
- pump, saddle bag, tube, multitool, tyre levers (Lezyne Road Drive pump $37, SciCon "twist to detach" saddle bag $20, tube $5, Michelin tyre levers $5, a minitool with a range of hex drivers and a chain breaker $30)
- front and rear lights (Planet Bike Blaze 2W $70, Planet Bike Superflash $40, plus AA charging system from supermarket $35). You'll want a better front light for winter (the Blaze is a good "be seen" light, in winter you'll want a "see by" light. Bicycle Victoria has an excellent annual review).
- well vented helmet, half gloves (whatever fits $150, whatever gel front, mesh rear glove you can find for $30)
- For 20Km per day you'll want padded knicks and a light rain jacket (Uno Pro Peleton Ghia knicks $60, jacket $50)
- The tyres which come with the bike won't be great, and depending upon the amount of junk on the road you'll want Gatorskin Hardshell ($45ea) or equivalent (there's a lot of mindless allegiance around tyres based upon personal mishaps, you want a high technology "training" tyre in whatever brand appeals to you).
That's $670 of odds and sods. Obviously the way to do this is a little at a time, with only the most essential stuff on Day One. The various internet sites are good places to locate accessories at a fair price. I've found that if you ask people to give you stuff for your birthday then mail them the URL of the item you want rather than say "a jacket" otherwise they'll either be ripped off or will buy something too nasty to be usable (probably spending more than the sale price you found on the Internet for buying the real thing).
Later on, an upgrade to "clipless" cycling shoes and pedals is worthwhile. Commuters use Shimano's SPD system with double-sided pedals (both sides having clips means less fuss when starting from traffic lights), along with light touring shoes (rather than heavy MTB shoes).
Edited to add: also bike lock ($80), track pump ($40), cleaning equipment ($40). Basically the first year of cycle commuting costs the same as using the car, but you win forever after that.