Here are some general stat's for all Somerville condo's that have sold in the last 6 months:
Condominium Listings: 305
Avg. Liv.Area SqFt: 1,179.35
Avg. List$: $412,079
Avg. List$/SqFt: $362
Avg. DOM: 59.67
Avg. Sale$: $408,473
Avg. Sale$/SqFt: $359
Get yourself an exclusive buyers agent (NOT the agent who is listing the property) and they will guide you through the entire process including value.
More stat's where the above came from:
Massachusetts Premier Buyer Brokerage
Everything for sale in Somerville:
I don't actually see any active listings for $450k in Somerville in MLS -- is this a for-sale-by-owner?
Hard to advise on price without knowing which property you're referencing, but in general, I can tell you that inventory is very low right now, and demand is high, so most condos are selling close to, at, or even over the asking price. Here's a link to a blog posting I wrote on this trend:
A good buyer's agent will be able to help you determine what offer price and terms make sense. If you don't have a buyer's agent and would like some help with this, feel free to get in touch -- firstname.lastname@example.org.