One bedrooms under 1,000 in a bunch of buildings east of Yonge downtown. Of course, quality in most is questionable if they're that cheap. Outside of the core, north of St Clair and Yonge has a bunch of buildings with one bedrooms for under $1,000. Bathurst and St Clair is even cheaper and you can find more around $900. My building south of Bloor West Village rents one bedrooms for $845, and it's a quality building, but few amenities within decent walking distance (but good transit, 501 at my door almost).
Annex has some cheaper buildings, but a lot are filled with college kids. Up and down Avenue Rd there are plenty of good buildings, but transit is bus only unless you walk to the subway. East end on the Danforth actually offers plenty of options, but there are many poorly maintained buildings. Shop around. Beaches is cheaper than most people might believe, and it's serviced by the 24/7 501 Streetcar.
Really depends on your budget, quality of where you live and what you consider downtown. People living in the city generally think 'the core' when someone says downtown, but you might be willing to live a 20 minute subway ride outside of the core and save two hundred bucks on your rent (and be in a better building).
