Not sure what you consider a reasonable price, but in general, Boston can be expensive.
Here is a start: https://www.clarendonsquare.com/ It seems most of the guests really enjoyed their stay.
(One of my favorites in Boston) The "Back Bay" area is very beautiful with its brownstone homes and tree-lined streets. Historic and very pleasant to walk around and just to absorb the neighborhood.
You are "walking close" to many other lovely areas and sites
"Bordered by Copley Square and Newbury Street, the Public Garden and Boston Common, and the SoWa Arts District, the South End is synonymous with Boston’s high style, as well as its historic and trendy ambiance.
Copley Square, Newbury Street, and the Boston Common are just minutes away on foot. Whether you are here for a conference at the Hynes Convention Center, business in the nearby financial district, or to explore the sights of America’s favorite walking city."