Here are a couple of inexpensive places to grab a bite:
El Zaziummm (Mexican Food)
The menu is a creative mix of Mexican-Californian. The decor is recycled from anything and everything; you can dine in a carriage, sitting on the floor as arabs or even around a sand filled bathtub while you enjoy growing plants in washroom sinks plastered to the walls... quite eclectic indeed, made with anything you can find on a beach (beers cans, condoms, postcard, sand, etc) There are sometimes people doing tarot, mariachis. The servings are gargantuan, so much there are no desserts at all, none what so ever... Where you should find the dessert section on the menu it reads: "desserts : unbutton your pants instead!" ...and that's what you'll probably do after a "Monster": Le Monstre (so huge that if you eat all the plate, 'J'ai mangé le Monstre' which means ' ate the Monster') the biggest hamburger you've ever seen, to those who dare and succeed, a 10% rebate on your bill and an " ate the Monster" t-shirt.
Hamburger Mexicali, Fajitas, Hot dog Hollywood (bacon, merguez, cheese, mustard, tomatoes, lettuce with fries) ,1276 Laurier E., 598-0344; 4525 du Parc, 499-3675; 51 Roy, 844-0893). All on the Plateau Mont-Royal.
For quick crepes, there is a place called La Crêpe 2 Go on Rue Bleury, corner of Rue Shebrooke. It's a small mom and pop place and serves very good crepes and even better prices! They serve the crepes or paninis with fresh fruits. To top it off, they have italian gelatos and granitas. They only have a few of tables and a couple on the sidewalk, so don't bet on getting a place to sit down.
For one of the most consistently top-rated cheap eats in the local Montreal alternative newsweeklies, go to Puca Puca, a cosy, colorful, and casual Peruvian restaurant in the Mile-end district of Montreal (5400, boul. St.Laurent, corner St-Viateur), very popular among the locals. It's particular good for it's grilled fish dishes. The Shrimp Anticuchos is also very good. It does not participate in the Montreal "Bring-your-own -wine" restaurant custom; but the wines are fairly inexpensive by Montreal standards and are not bad.
Very nearby is the very famous Fairmont Bagels (74 Fairmount West). This is strictly a bagel bakery: you go to counter in front of the brick ovens and buy Montreal bagels fresh out of the oven (yum!). This joint is open 365 days a year, 24 hours a day (check out their website at http://www.fairmountbagel.com/). You can also buy cream cheese (recommend Liberte brand) lox, a pretty good salmon spread alternative and such. Besides just being an excellent spot to pick up one of the best examples of quintessential Montreal delights, it is the one of the traditional places to go after a Montreal night of clubbing or partying for an early, early breakfast before heading up to Mont-Royal to watch the sunrise, or staggering home to bed.
Another quinessential Montreal thing (to eat) is Montreal Smoked Meat (simillar to Pastrami). Pick medium fat, get a 'plate' (comes with a stack of rye) and make your own sandwiches (share with a friend) or just get your own heaping sandwich. The Absolute most important one is Schwartz's Deli (3895 boul. St Laurent; http://www.schwartzsdeli.com), and usually has a line going out the door at lunchtime. Anothervery good one is across the street called "The Main" (3864 St-Laurent Boulevard; open 24hrs). Still other good ones are Dunn's and Ben's Deli and Reuben', all downtown in the Golden Mile. Warning: not for vegetarian's or health food affcionaldoes.
A good place, since many years now a chain (that even sells prepared foods available at local Costco's), is the cafeteria-style sold-by-the-gram "Le Commensal", a vegetarian eatery. Great for quick lunching or dining before or after something else such as an exam, a meeting, a movie, the museum, or a place to have the meeting, or to study, whatever. The foods include a variety of things, like hot dishes with Seitan to Tofu to millet pie, pastas, pizza, soups, salad bar, desert bar, teas, etc. An old favorite amongst the locals. 1204 av. McGill College is one, 1720 St-Denis St (between De Masonneuve and Ontario) is another (among many). One may happen upon an oldie that still remembers the original location on St-Denis, with its mismatched furniture (now slicker interior designed), people would hang out all day and nibble, write poetry, draw, write, study, discuss; when the mission was to provide anyone with an affordable good meal (soup and unlimited homemade bread was a buck fifty at the time). Still is a pretty good choice though the ambiance has changed.