lazyboy, honestly, it's not going to be easy to find something in that price range.
At €380, this is one of the cheapest options I've seen:
http://www.locaflat.com/hostel.htmlYou might be able to find a
chambre de bonne for about the same price.
Even a shared apartment often goes for 500-600 euros apiece. Paris is definitely not a cheap city to live in. Also take into consideration any utility charges and deposits as well as the location, which may affect your transportation costs.
Check out
Particulier à Particulier (
http://www.pap.fr) for rentals (
locations) and shared rentals (
colocations). Also check with the school you'll be attending to see if they have any suggestions regarding inexpensive lodging or lists of potential roommates.
Good luck!
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p.s. I just searched for 1-room apartment rentals in the PAP and found one in the 6th arrondissement, 6th floor (WITH elevator, believe it or not), furnished, for €220, charges included (WC on the landing but no mention of shower--you'd need to ask whether there is one as often in those small rooms there are not). There's another listed for €240 with shower. one for €280, some in the low €300s, and others on up from there. Don't expect luxury at those prices, but evidently if you search and have a little luck you might find something to fit your budget.