My first question would be, what qualities make a school great in your opinion? Real estate agents aren't qualified to evaluate a schools qualifications. You'd have to consult the Mass Dept. of Education website for school qualifications and make your decsions from there, there are also alot of 3rd party school rating websites out there also.
Next comes finding a 3 bedroom home within 30 minutes of Lexington and especially a low price of $280K or less. There are fewer options out there with such a low price. Give your parameters you will probably have to compromise either home size, school ranking or other features.
Now the good news, given the current market, now is actually a great time to actually find such a home. Just a year or 2 ago those parameters might have been an tall order. In my opinion and perhaps a personal bias take a look at Medford. You could also look into Woburn, Reading, Stoneham, Billerica, Burlington, Waltham etc. Finally in other states 30 minutes drive can cover quite a distance, here in the Greater Boston area that can be a very short distance due to traffic, road conditions, weather and Massachusetts drivers.
Good luck in your search, it'll be great to have you as neighbors :)