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Wow, under 10 Euros is really pushing it if you want a menu, your best bet would be the ubiquitous vietnamese places that also do take-away (there's one on every corner, and the food is edible, good, even;). You may be able to find a cheap couscous near your place in Bagnolet as well (I don't know the area). I'll ask around and see what I can come up with.
In Montmartre, there's a café restaurant I really like (I love their lasagne, but they have more French stuff as well), but they are more in the 20 Euros range : it's called Un Zèbre à Montmartre, 38 rue Lepic, 18e. In Le Marais, I love the (very filling and delicious) sandwiches and jewish food at Sasha Finkelstein on rue des Rosiers (4e), not to be missed.
Are you planning to go to concerts as well ?