The main reason for lower prices in Maynard has to do with the size of the houses and size of the lots. Maynard is a small town with a population of just over 10,000. The total area of the town is only about 5 square miles, of which only 3.5 miles are buildable so the houses tend to be smaller than in the surrounding towns; the lots sizes are definately smaller - some on as little as 4,000 square feet of land - a half-acre lot is considered large, so the town is more densely populated.
Also, the housing stock tends to be older - lots of early 1900 homes in the downtown area near what was originally the Maynard Mill which was Digital Equipment headquarters in the 70s and 80s and now home to Clock Tower Place which has approximately 80 companies including Monster.com and Curt Schilling's game company. Certainly there are newer homes further from the downtown area, but again, not of the size you'll find in the surrounding towns. The housing is more diverse and includes single family, multi-family, and some apartments, whereas the surrounding towns tend to be mostly single family homes of acre, acre-plus lots - a suburban environment.
Maynard has some great things - restaurants, a movie theater, art studios, small shops in the downtown, a new library, an old-fashioned ice cream stand, hiking trails, a golf course, band concerts, sidewalks, streetlights, a new police station, town water and sewer. And although there are not major highways going through it, it is very centrally located; accessible to many places via route 117 and route 2, 62 and 27. And you can enjoy the surrounding towns - Concord, Acton, Stow, and Sudbury.
Hope that answers your question.