Delphyne's apartment is an excellent budget option in Belleville.
We spent 6 very good days there at Christmas time.
It's very close to two metro stations (we suggest getting off at Pyrenées so you just have to walk down the hill to get to the apartment and consider leaving via Belleville, so you also just walk down the hill). The restaurants in the area are to die for! Try the poulet au gingembre at Lao Siam, just two buildings next to the apartment. In the neighborhood you'll also find many options of supermarkets (Monoprix, Carrefour, Franprix just a few blocks away) as well as grocery stores.
The apartment has excellent heating, the shower has really good hot water, you'll find a very complete kitchen (though we only had breakfast in).
Mind that you have to walk up three floors to get to the apartment, we found that ok, but some people might have trouble with that.
The only downside is that the apartment seems to build up moisture, so the towels smelled like they didn't dry fast enough. Manageable, but that was the only thing that might be improved.
I think staying here is a great budget option, and Belleville is a whole new Paris (we had previously stayed at Passy, La Chapelle and near the Arc de Triomphe).