I've read a lot about Mexican over the years. Fortunately, the quality (and variety) has improved in Toronto over the past few years with the likes of Playa Cabana, Grand Electric etc.
For a simpler, and very authentic (and casual) experience, I highly recommend:
1) King's Taco (St Clair W, just west of Dufferin)
The owners are extremely pleasant, and bring a chain (or 4-6?) restaurants from Chihuahua state in Mexico. The flavours are strong, and tasty, the portions are very generous, as are the massive amount of complimentary "real" nachos with 3 salsas they give you prior to dinner. Avg price is $11-14.
FYI- no alcohol.
2) Tenoch (St Clair W, just east of Oakwood).
Service has been a bit slow, but I feel its worth it for their food. Just like above, very casual atmostphere - they may have a few other dishes that KT doesn't, plus sometimes I like eating 3 tacos instead of the 4/5 that KT serves. No free apps though. At least there are cheap drinks. Avg prices $10-15.
I've eaten at KT about 7-8 times (so-so busy during week, PACKED on weekends), and Tencoch 4-5 times, always fairly busy, but closes at 730 Tues-Thurs(!), 1030 I think weekends. Both have a very strong Hispanic patronage (if that means anything to you).
Even though they are simple restaurants, I totally think that it's worth the drive/TTC up to check both out as they are standouts to most of the competition.