Somerville Road Runners has a lot of weekly runs. There's also Cambridge Running Club, but their setup doesn't sound like what you're looking for (they do a track workout on Thursdays and a long run on Saturdays). And a lot of local breweries have runs -- like I know Remnant Brewing in Union Square has a weekly run night.

Broadway Marketplace (the overpriced little grocery store near the public library) gives rolls of quarters.

I go to Cambridge Cat Clinic. Last year, my cat's yearly checkup was $75, plus another $60 for vaccines.