We are in the grip of a "loneliness epidemic" where social isolation carries a mortality risk equivalent to smoking 15 cigarettes a day. 

As part of a recent city inspection on a duplex we bought, we found out the city fire code is for the smoke and CO alarms to be interconnected (including hardwired in the basement). 

When I opened the front door, a wall of cigarette smoke and pet odor hit me.

The $385 for bulbs and filters feels like a lot of "fluff" labor.3. $66 per smoke detector seems steep for what are likely basic 10-year battery units.Am I overreacting, or should I be shopping this around?

We havnt been able to tour the tenant occupied side yet, not until we have an offer accepted, but when we were touring the property in general I noticed the front yard of the tenant side absolutely littered with cigarette butts, which makes me a little uneasy about the quality of the tenant.

There are smoke alarms though.

Small things—GFCI outlets, handrails, window locks, smoke/CO detectors—can delay move-ins if they’re not addressed upfront.

No exposed wires, solid railings, working plumbing, proper outlets, smoke and carbon monoxide detectors, reliable heat.

IMO the price is very high.I toured the home, the sibling I know staying there clearly is smoking weed, and the carpet has not been replaced. 

Even well trained pets sometimes have accidents, and, while they may "look" fine  when you inspect a carpet at move out, a couple good hot days of sun coming through the windows on the vacant unit and you often discover new odors or stains wicking back up through the carpet.Just like "No Smoking" units, whichever way you go will cut you out of a percentage of the market.