Not exactly sure how you're calculating that $100 out of budget etc...but use http://www.bankrate.com for good info and an amortization calculator, which is very helpful.
Keep in mind, unless you put 20% down you won't get the best rate, will likely have PMI or pay a higher rate to not have it, and will have to escrow taxes and insurance until you are below 80% LTV.
Being your first house I would say sacrifice somewhere to keep it affordable, you don't want to "lose" your first house because you can't afford it and then screw your chances of really affording and enjoying your dream home down the road.
Also, be aware of property taxes, you can use the auditors website to estimate them based on a certain value, but figure another $4-5000/year on annual property taxes and property insurance, depending on the home value and location. Some pay it monthly, some pay it annually, and it WILL go up. My homeowners insurance has gone up nearly $100/year for the past 3 years, it sucks but is what it is.
And utilities, I'd figured them doubling from an apartment to a house, at least mine about have, so make sure that's in the budget.
Good luck, I bought my first place in 07 and wouldn't have changed a thing, luckily I've done well in this market and still have plenty of equity, a good interest rate (refi'd), and a comfortable payment.