Do a search for the same topic. Generally speaking, though, there are no schools in Canada, so you're looking at the States. Cheap they ain't either. Then you'll have to find a very scare job. Like all other trades, nobody wants anybody with no experience and the pay scale is low.
Forget the correspondence schools too. You'd need a sample of every firearm they talk about in each lesson. That is expensive.
On the other hand, learning to do some smithy jobs for fun can be done with books and junker firearms.