Places like Chelmsford, Boxford, Topsfield, Andover, and Middlton have great school systems but tax and home values are a lot more. North Andover, Haverhill, and Methuen are locations that have average rated school systems, but you will get a lot more for your money especially with a $500k budget even though the median list price in methuen is close to $240k. If you search for any town/city in the search homes tab on the Redfin website you can click on "stats and trends" on the left side. Under stats and trends you can get current market trends, price reduction meter, median sold price, school ratings, and more.

Hope That helps