Being both a realtor and a resident here in Chelmsford I must unfortunately tell you that newer built homes in the $300-350K price range will be very limited. Newer built homes in Chelmsford tend to be in the $500-700K price range. However, there is a newer development in Chelmsford called Lamplighter Green. These homes fall in the $300-$350k range and were built about 10 years ago. I specialize in Lamplighter Green and have sold many homes there. Unfortunately, there are no homes currently for sale in Lamplighter but the spring may bring some new activity and I can certainly alert you if any homes come on the market.
Lastly, I understand your desire for a newer built home but I would not discount older homes. There are many older homes that have been well-maintained, updated, and upgraded that would give newer homes a run for their money. So, I would not let Chelmsford's lack of newer built homes in your price range dissuade your Chelmsford search. Chelmsford is a wonderful community that offers an excellent school system. If you are interested in Chelmsford, I can happily answer any other questions that you may have.