I see where your head is at....buying a SF is better than nothing....but I would advise you to instead expand your search area to include more affordable communities that are still accessible via the commuter rail. As others have mentioned, there is some better opportunities once you travel 30-45 mins outside the city.
Not that owning a SF is bad, but if your thought is that you can start building that equity to help with future purchases I would caution you. If your suspicion is that the market is in a bubble (maybe right), it will impact the SF's just as much as the mf's. So, if you hypothetically buy a SF today, pay down your debt for 2 years, and the market turns, at which point you try and do a HELOC/home equity line/refi you are still in a tough spot as your value has diminished and that equity you are looking to tap into is no longer there. If you do go down this road, my advice would be to think long term no matter what you do so you can ride out any bumps in the road.