Isn't J&J helping you with this? I interned at Kraft just for a summer and they set us up with apartments. They paid pretty well for an internship (not much less than a starting salary with a BS) so I'd think that J&J would do the same.
Somerville probably is the cheapest town. Just not sure how many people are looking to give out 6 month leases. There are some not-so-great areas of Somerville though (south of the main street going toward 206) so just be a little careful. Somerville has a nice downtown area and would be a nice place to live otherwise.
Claremont Towers in Hillsborough
http://www.claremonttowers.com/ also has 6 month options and would be pretty central to Skillman and Somerville.
I thought Pike Run in Montgomery had some corporate apartments which might work. I know it's not a cheap complex but it's safe and convenient if J&J could hook you up with anything there.