Pho Soups in Mississauga
I like Pho Mi 99 in the new Shopper's Drug Mart plaza just east of Mavis / Burhamthorpe. Everything I've ordered has been good and fresh, one big bonus is that it's within walking distance so I find myself eating there often. Another place I like is pho Kim Phung, it's tucked away in the Chinese plaza on Central Parkway West / Burnhamthorpe. If you know where Executive Snooker Club is, it's the restaurant 1 door down.
Prices are pretty standard ($4-$6 per dish) at pho shops. Start off with the standard rare beef pho, or even try the beef with tripe pho if you're open minded. Definately wallet friendly eating.
There's a few 24 hour pho shops in the Dundas Hurontario area, I don't find them that great - but they're pretty convenient coming home from downtown late at night when everywhere else is closed.
There's more than just pho though, try the chicken/pork chops on rice or vermicelli dishes, definately a good pick for your first time.