Plus there may be issues that are specific to your house.

Not even in a low cost living could you do that for that budget. Renovations start at double new construction prices. New construction starts at roughly $200 sf. Double your budget, at a minimum, to start.

Depends on your location, my friends put in an addition for a bedroom , small common space and a full bath for much less than that.

Where you live will drive the budget to some degree where I live that with very simple choices would be 120K for a start.You will need ana rchitect anyway so start there.

start with an archietect design the project first then do your cost yes it depend on is it upstair s addition and first floor as well that all matters if you need an archeitect we can recomend no strings attached you can pick your contractor