Set up a spreadsheet with this formula, it will give you a ballpark figure:
=(House Price-Down Payment)*(Interest Rate/12)/(1-((1+(Interest Rate/12)^-(Length in Months))
so for your numbers (assuming 25 years):
(300,000-10,000)*0.25%/(1-(1.0025^-300)) = $1375 per month
or $635 Bi Weekly.
If you need to add any mortgage insurance you add the amount onto the first bit, the total being borrowed.
Then Goal Seek away!