If you want to maximize your speed to shorten your commute time while not working to hard, something with skinny slick tires would be best. If you want to be a bit more comfortable and don't mind your commute taking another 10mins then a skinny tire towny bike(like a mountain/beach cruiser cross bread) would be best. The town will suck for future group riding with road riders you meet so its going to be a commuter and earned runner only.
How much are you will to spend and are you mechanically inclined?
No harm in talking to your LBS and getting to know them because Chandra are you'll be back there for repairs or parts sometime in the future. Talk to them get some info on the type and level of bike they think will suit your needs then take a look at your local Craigslist and see if there's anything that matches what they suggest at a better deal. Try haggling with your LBS on your second or third visit after you know a bit more, its 50/50 wether they'll drop the price much but it happens from time to time. Called up a shop and BSed them and got a $6500 bike for $4000 and it was a special order they had to bring and build for me. A year later my dad drags me to another shop to buy a bike for himself, they won't budge from the $2200 sticker so while he's haggling I call up the shop that hooked me up and bam $1900 for the same bike, Sold
Between my dad and my self we have 5 bicycles each worth nearly twice as much as the Ninjette. But we all started on bargain bin stuff in the past to get up to speed. I worked my whole summer vacation of my sophomore year in high school just to by my first Mtb of my own(not a gift from the parents). It was a trek 8500 alloy hardtail for $1000, the thought of buying a my first car never even crossed my mind
