Maybe I’m crazy, maybe I’m a bit of a homer, but you should consider Northern Virginia (Arlington and Fairfax Counties) or Bethesda/Silver Spring, MD.
**Cost of Living: **The obvious downside is that certain areas are pricey. Depends how close you are to the metro/subway and the center of DC or Arlington, or Tysons Corner.
**Swim: **However, these areas all have good public pools (county pools in Arlington and Fairfax, and YMCA, etc. in Maryland).
Biking: I for one am a big fan. As biking goes, depending on exactly where you are, you’ll be 5-15 miles of bike path to Montgomery County, MD or the rural parts of Loudon and Fairfax counties in Virginia which have nice country/suburban routes. Except for the coldest weekends in December-February, you can ride outside all year (summer gets muggy, but the evaporative cooling effect of biking mitigates most of it). Also only about 1-1.5 hours from Shenandoah valley which is spectacular (lookup Skyline Drive if you haven’t seen it before).
**Running: **Nothing like Boulder but plenty of trails and parks, and high density means lots of local tracks to get in more structured workouts.
**Support/Social: **Tons of bike shops, tri clubs, etc. in the area. Not great for open water swimming practice though–but with the quantity of local races, you could realistically swim open water once every couple weeks April-October.
**Race Opportunity: **Tons of local races and relatively close to the IM circuit with Chatanooga, Wilmington, Virginia, Maryland, etc. all hosting events. Kinetic Multisports puts on more events than you could possibly attend in the Virginia, Maryland, Delaware, Pennsylvania region: practically one every weekend and they are affordable (~$100 per race).