3 in total.
It is common for Senators to have at least 2 residences, one in their home state and 1 in DC.
He paid for his home state home the same way as everyone else. (4 bedroom, 2.5 bath, $405K)
His DC residence is a town house. (1 bedroom, 1.5 bath, built 1800’s, $489K)
His 3rd property is a small lake side cottage. (4 bedroom, $575K)
To
afford it, his spouse sold her share of her inheritance house built in
the 1800’s [she came from a wealthy family] to one of her siblings,
Bernie used the wages obtained from his best selling book, and they also
dipped into their retirement fund.
After
his 2016 run and subsequent book deal, Forbes put his networth at $700K
though estimates varied and his current networth has been placed higher
as the proceeds of the book deal come in.
Of the initial estimate, much of that is attributed to his Vermont home as he owns that one outright.
https://www.quora.com/How-did-Bernie-Sanders-get-all-his-houses-and-how-many
https://www.quora.com/How-did-Bernie-Sanders-get-all-his-houses-and-how-many