All three iPhone carriers offer pretty much identical plans. The phone cost is dictated by Apple, so it will cost the same everywhere.
At $60-70 a month, there's not much to work with though.
I suggest Fido, because they bill by the second. Here's the lowest iPhone plan they offer:
250 daytime inutes
Free evenings/weekends from 7pm
Unlimited picture messages
500mb of data
Call waiting and conference call
$65 + tax = 73.45
If you want caller ID, it's an extra $7.
$65 + 7 + tax = 81.36
Current arsenal: iPhone 5S 16GB / 13" Retina Macbook Pro 2.5ghz 8GB ram / iPad 2 WIFI 16GB / Apple TV 2 / Slingbox Solo / Acer Aspire Z5610 touchscreen all-in-one / Acer Aspire netbook
Fallen soldiers: iPhone 5 16GB / iPhone 4S 16GB / iPhone 4 16GB / iPhone 3G 8GB / BlackBerry Pearl 8100 / Motorola L6 SLVR / Nokia 5190, 3390, 8390, 3220 / Ericsson T18z / Mitsubishi G310 / Motorola C333 / Sony Ericsson T237