I'm not sure about monthly costs, because that's a very personal thing... There are shelters where you can get free food in the mornings if you really need to, buses to avoid racking up gas prices... All sorts of ways to cut costs! But for housing, I have a lot of info. Here's a brief overview, because I have lived everywhere, lol:
First of all, the whole area is pretty liberal. The only problems I run into with people come from undergrads. They're pretty easy to avoid, though.
Northampton is a wonderful town! It has an awesome scene, lots of bars, independent stores, coffee shops, music halls with lots of performances... And it's where Questionable Content (the webcomic) takes place! And I personally like Diva's, which is a gay club that a lot of students and locals go to. Lots of fun! Because of the area, it's pretty accessible to meet people of the same sex (not sure if you're looking or not)... The people are generally awesome! But since NoHo is a bit far, and can be a pain to commute to / from, you might want to consider the Hadley area, somewhere between UMass and Northampton. (Plus, Hadley is a bit cheaper!)
If you lived in Hadley, you'd be near all the stores you'd need. The bus to UMass from there isn't as regular as some others (some come every 15 minutes and since places might be on a route with two buses, it's like every 8 minutes; Hadley's bus is every 20 minutes during normal hours).
As for costs: if you're willing to, say, take a private room in a house (spots which the locals usually give preference to grad students), it's usually between $350-500, depending on location. Regular 1br apartments can be $700-900. That being said, there are a lot of places where you can split 2br apartments for prices like $300-500, depending how nice a place you want. There are reliable apartment complexes in the area, so you can expect similar rates around.
Sunderland is another town nearby with a bunch of housing and apartments, but it's also a longer trip to things like the grocery store at that point. That being said, it's freakin' beautiful around there; farms, mountains,... It's only like 15 minutes from campus, but more like 20 to the stores. It's quieter, there aren't as many party-hardy undergrads out there; in my experience, it's more seniors who are ready to graduate, and non-students.
[bUT HOLY CRAP DON'T GO TO SUGARLOAF ESTATES. They look nice. They're a nightmare. If you seriously consider them, please message me first. I have warnings to give.]
North Amherst is awesome if you go far enough. It's close enough to regular buses, but still just out of ugrad party distance. But the string of apartments just north of campus is an undergrad party zone. By your description, you do not want to live there. If you're interested in North Amherst, make sure it's at the border of or beyond Pine Street.
Are you bringing a car? A pet? A roommate?
And here's the UMass housing resource, if you're interested (I've never used it): http://www.umocss.org/