I came here in Summer 2013 (twice) and I loved it! Their prices are very reasonable and I ordered take out twice because I didn't want to wait for a table. The restaurant is very small and can only seat up to around 15 people I believe.
The burgers are very cheap (I believe around two bucks) so ordering two will fill you up easily. Their fish burger is also very tasty and their poutine is decent. The walk from central Montreal is perhaps 15-25 minutes so I feel like it's worth it since there is a lot to see on the way to this restaurant.
The restaurant is actually pretty hard to spot because the name is kind of hidden so you might want to look it up on google images to prepare yourself. (or just use GPS on your phone if you have data) Patati Patata is the epitome of the term "cheap eats" and definitely should be visited by anybody, not only people on a budget!