Hey Tim,
I'm currently in the process of becoming a licensed lead paint inspector in the state of Mass and am starting the last phase which is the apprenticeship. I've gone through the required class trainings and have passed the state exam. So I'm not 100% official yet, but I think I can get you pointed in the right direction. There's a lot in your post and to cover on this topic, but I'll try to hit the major points. FYI...I also own rental property in MA.
Congrats on the purchase!
First step would be to look the property up on the MA Lead Paint Database (https://eohhs.ehs.state.ma.us/leadsafehomes/defaul...). This database keeps track of all properties that have been tested and abated. It's always good to check on a property you're interested in to see if it has any history. I'm going to assume that it doesn't and it has never been tested.
Like you allude to, with the age of the housing stock in MA, it's more likely than not you'll find lead paint. I'm not sure where you got some of your information, but some of it is right and some of it is leading you astray. First...let's cover the law.
In MA, property owners are REQUIRED to bring a property into a lead safe condition (called compliance) if a child under the age of 6 resides in the house/apartment. If a child under 6 is poisoned in a property you own, you are 100% liable under MA law. It's called strict liability and it's what gives the MA lead paint laws such big teeth. We have the strictest lead paint laws in the country.
Good news tho, the State of Mass just made a major revision to the lead paint laws that went into effect on Dec 1, 2017. One of the keys for landlords is that the new rules significantly lower the number of surfaces that have to be deleaded...which lowers the cost of abatement compared to the law pre-12/1/2017.
As for your property, I don't know how a deleading contractor can give you a quote without an inspection report. Only MA licensed lead paint inspectors can perform an initial inspection which will determine what, if any, lead hazards are present in the house. The cost of this can vary quite a bit based on a number of factors, but especially if the property has older wooden windows (it can take a while to test all their components). My guess, would be it'd cost between $750-1250 to do the initial inspection. One thing you have going for you is the apartments are vacant which makes the testing a lot easier.
After that, you can give the report to any deleading contractor and they should be able to give you a quote based on what's found. It's really hard to come up with a cost because it really depends on what work needs to be done. I had a single family I own done last summer and it cost me $1500 to scrape a bay window sill, an exterior door edge (on 3 sides), a threshold, and have 4 basement windows covered/wrapped. Something to note is that not all work requires a deleading contractor. Scraping and replacing windows (called high risk deleading) are examples of work that would require a deleading contractor. Things like covering a wall with drywall if there's flaking lead paint is something a low or moderate risk authorized owner could do. You just need to do some reading and/or a class plus some tests to get certified. It depends on the hazards that are found but can save you some money. The inspector can give you a lot of the options you have.
The contractor you talked to is right when he says cleaning is a major part of the work they do. To get a letter of compliance after deleading work is done, the lead paint inspector needs to come back and take dust wipes, which are sent to a lab to make sure there isn't high levels of lead paint dust left behind. The main focus is rooms where work was done, but other rooms are also tested during this process. After those dust wipes pass, you get your letter of full deleading compliance.
You did get good advice on NOT doing the work yourself (if not authorized) or not having a properly authorized deleader do the work. If the work is done as a deleading activity and not as regular renovation, an inspector is required to call this out on their report which can be flagged as "unauthorized deleading." If the state deems the work to be unauthorized deleading, it can prevent the property from ever being able to get a letter of compliance. Just be careful.
Sorry...I know that's a lot of information, but there's a ton of topics to cover on this to make sure people get going in the right direction. If the property is one that makes sense for families to rent, if I were you I'd really think about getting it tested and deleaded. I know with the single fam that I own, it gave me a lot of piece of mind when getting it listed. It also helps the value of your property.
One last thing in terms of cost...MA does offer up to a $1500 tax credit per unit for work done towards deleading, so you'd be eligible for up to 3k in MA tax credits. It's not going to take the biggest chunk out of the cost, but it's a little be that helps.
Hope that helps Tim. Feel free to fire back with other questions you might have.
Rob