Hi Diverging Artist.
We live in South Western Ontario - not far from where MMM grew up. We keep our cost down the following ways:
My wife is a SAHM. This is the biggest factor in keeping costs down as a family. We have one car (a nice 2008 Mazda5). She also makes most of our food from scratch, grows an extensive vegetable garden, hangs laundry, watches for prices at the store and stocks up when a big sale is on. If she was working in a career there is no way our expenses would be only 30k.
Other factors are low property taxes (2k year), a fairly small house, live close to work etc. No cable, pay as you go cell plans (Fido for $99/year!)
We do have our kids in activities - all fairly low cost ones through the Y or local community center. Also 2 are in soccer and one in baseball. Each costing only $150 for the whole season.
Here in Ontario there are no individual health insurance costs - but taxes are a little higher than I like. However, with the new income splitting measures for families the fed implemented - it will make it that much easier.
In terms of investing, we max our every tax leverage account possible (our RRSP's, TFSA's and RESP's are maxed out)
Hope that helps and is bad-ass enough!