Typically I would say that if you're riding 2 or 3 miles, then anything will do including 50 pound tanks.
However, as a small person carrying the bike up stairs, the lighter the better. I've been commuting on an ex-racing bike for years. Steel, mid 20's in weight, I think (that was the standard when it was bought).
It is tough to get a cheap bike under 20 pounds, but 22 or 23 pounds is very doable, especially if you start browsing the used market, and know what you're looking for.
What is your security like at the office?
As far as the performance of a racing bike for commuting. You do have to worry about glass and road obstructions. But otherwise they are just fine. Two miles? You can get to work like greased lightening!!! Perhaps one of the few people that could actually average 20+ MPH for their commute
Originally Posted by
Giant Doofus
Have you thought about a folding bike? That would make it much easier to get up the stairs. On the heavy end, I think folders weigh about 25 pounds. You might look t the entry level Bike Friday.
I was thinking about something like that, or perhaps a Brompton which can be drug around like a piece of luggage with wheels.
You'd be a little over budget, but it might be a good bike to splurge on. And, the claims are that the high-end folding bikes are just as good as the normal "road bikes" for taking out on the road.
If you do choose a conventional bike, post your location and some links on Craigslist, and people will surely give you a thumbs up or down, and maybe some new suggestions.